Sweet Caramelized Onion & Mushroom Potato Tart

Indulge in the rich, comforting flavors of this exquisite Mushroom, Caramelized Onion, and Mashed Potato Tart. This savory masterpiece features a meticulously prepared, flaky all-butter pie crust, generously filled with a harmonious blend of creamy mashed potatoes, tangy goat cheese, beautifully browned mushrooms, and deeply flavorful caramelized onions. Baked to golden perfection and garnished with fresh thyme, this rustic tart transcends expectations, serving as an impressive main course, a delightful side dish, or an elegant appetizer for any gathering. Its robust yet refined profile makes it a versatile addition to your culinary repertoire, promising to captivate taste buds and leave a lasting impression.

This potato tart, highlighted by the piquant notes of goat cheese and the earthy aroma of thyme, is more than just a dish; it’s a culinary experience designed for any occasion. While we affectionately call it a tart, its adaptable nature allows it to be equally described as a savory pie or a free-form galette, much like our popular caramelized onion tart. Its inherent flexibility extends to its preparation: traditionally baked in a sturdy cast iron skillet, it can also be effortlessly crafted on a simple sheet pan, making it accessible even without specialized tart pans or pie dishes. This adaptability ensures that whether you’re a seasoned baker or a novice, you can achieve a stunning and delicious result.

At its heart, this rustic and utterly delicious tart begins with a foundation of flaky, buttery pie crust, a testament to homemade quality. This golden base cradles a luscious layer of seasoned mashed potatoes, which provides a creamy contrast to the other textures. Generously sprinkled atop are dollops of soft goat cheese, offering a delightful tang that cuts through the richness, though options like crumbly Gorgonzola or grated Parmesan can also be used for varying flavor profiles. These are then layered with deeply browned mushrooms, imparting a rich umami depth, and sweet, jammy caramelized onions, whose slow-cooked sweetness is simply irresistible. A final flourish of fresh thyme leaves elevates the dish, adding an aromatic touch before it’s baked until the crust achieves a beautiful golden hue and crisp texture.

Upon slicing into this magnificent creation, you’ll be greeted by distinct, visually appealing layers of each component. The magic truly happens when these individual flavors and textures unite on the palate – a symphony of crunchy crust, creamy potatoes, sharp goat cheese, earthy mushrooms, and sweet onions. Each bite offers a perfect medley, combining crispiness, creaminess, a delightful tang, and subtle sweetness, creating an irresistible urge to reach for “just one more bite.” This harmonious blend of tastes and sensations makes it an unforgettable dish that consistently delights.

Looking for more savory inspirations? Explore other delectable recipes from our collection, including the vibrant Spinach and Smoked Salmon Quiche, elegant Prosciutto Asparagus Puff Pastry Bundles, classic Ham and Swiss Quiche, flavorful Sausage and Boursin Stuffed Mushrooms, and charming Cheese Tartlets. Each offers a unique savory experience, perfect for expanding your culinary horizons.

Essential Ingredient Notes for Your Savory Tart

Crafting the perfect Mushroom, Caramelized Onion, and Mashed Potato Tart begins with understanding its core components. Paying attention to these ingredients will ensure your tart is bursting with flavor and boasts an irresistible texture.

• The Pie Crust: A Foundation of Flakiness. This recipe champions a homemade all-butter pie crust. While store-bought options exist, we wholeheartedly recommend making your own. The all-butter crust delivers unparalleled flakiness, a rich, melt-in-your-mouth texture, and a depth of flavor that complements the savory filling beautifully. Its slightly larger size when rolled out is also crucial for accommodating the generous layers of ingredients, allowing for that signature rustic folded edge.
• Mashed Potato Layer: The Creamy Heart. The mashed potato layer is designed for ultimate creaminess and flavor. We use starchy potatoes like Russets, which yield a fluffy interior perfect for mashing. Enriched with generous amounts of butter, a splash of milk for silkiness, and a dollop of sour cream for a subtle tang, this layer forms a comforting base. Proper seasoning with salt and pepper is vital to bring out the potatoes’ natural sweetness. Ensure the mashed potatoes are cool before assembling the tart to prevent the crust from becoming soggy.
• Mushrooms: Umami Powerhouse. Standard button mushrooms (cremini or white) are excellent choices for their earthy flavor and accessibility. However, feel free to experiment with other varieties like shiitake, oyster, or a wild mushroom blend to add more complexity. The key is to brown them thoroughly in a hot pan, allowing them to release their moisture and develop a deep, caramelized umami flavor. This browning step is crucial and elevates the mushrooms from simple fungi to a rich, savory component.
• Caramelized Onions: Sweet & Savory Depth. Two large yellow onions may seem like a lot, but they cook down significantly, transforming into a sweet, jammy, and deeply flavorful condiment. The slow caramelization process, taking about an hour over low heat, develops complex sugars, resulting in a sweetness that beautifully balances the tartness of the goat cheese and the earthiness of the mushrooms. Patience is truly a virtue here; do not rush this step, as it is foundational to the tart’s unique flavor profile.
• Goat Cheese: Tangy Counterpoint. Fresh goat cheese adds a creamy, tangy, and slightly tart element that brightens the entire dish. Its distinct flavor pairs wonderfully with the sweetness of the onions and the richness of the potatoes and mushrooms. If goat cheese isn’t your preference, consider alternatives: Gorgonzola offers a sharper, more pungent flavor, while Parmesan provides a nutty, salty depth. Adjust the quantity to your taste, but a generous sprinkle ensures a balanced flavor.
• Fresh Thyme: Aromatic Finish. Fresh thyme is not just a garnish; its subtle, peppery, and earthy notes infuse the tart with a fragrant aroma and taste. While dried thyme can be substituted in a pinch, fresh sprigs scattered before baking, and a few fresh leaves after, will provide the best aromatic impact and visual appeal.

Crafting Your Mushroom, Caramelized Onion, and Mashed Potato Tart

Creating this magnificent savory tart is a process of layering delicious components, each contributing to the final harmonious flavor. With a little planning and patience, you’ll achieve a rustic masterpiece.

⏱Timing Tip! To streamline your preparation, consider making the pie dough, caramelized onions, mushrooms, and mashed potatoes a day in advance. Store them separately in the refrigerator. This allows for quick assembly and baking on the day of serving, making this impressive dish surprisingly convenient for entertaining or busy weeknights.

STEP 1: Prepare the All-Butter Pie Crust. Begin by making your all-butter pie crust according to the recipe instructions. The key to a tender, flaky crust is using cold butter and not overworking the dough. Once prepared, wrap the dough disc tightly and allow it to hydrate and chill in the fridge for at least 2 hours. This resting period is essential for gluten relaxation, which prevents shrinkage during baking and results in a more pliable, easy-to-roll dough.

STEP 2: Caramelize the Onions to Golden Perfection. Peel and thinly slice the yellow onions. The thinner the slices, the faster and more evenly they will caramelize. Heat a large skillet over low to medium-low heat, then add a tablespoon of olive oil. Add the sliced onions to the pan, tossing to coat them evenly with the oil. Reduce the heat to low and cook slowly, stirring occasionally. This patient process allows the natural sugars in the onions to develop, transforming them into a deep golden-brown, sweet, and jammy consistency. This usually takes about an hour. Resist the urge to rush the process with higher heat, as this can lead to burning rather than true caramelization. If you notice them sticking or browning too quickly, add a tiny splash of water to deglaze the pan and lower the heat further. Once caramelized, transfer the onions to a bowl and allow them to cool completely.

STEP 3: Brown the Mushrooms for Deep Umami. Clean and quarter your mushrooms (or roughly chop larger varieties). For optimal browning, ensure the mushrooms are dry; pat them with a paper towel if needed. Heat a large, sturdy pan (a cast iron skillet works wonderfully here) over medium-high heat until it is very hot. Add a tablespoon of olive oil, then the mushrooms. Toss to coat and spread them in a single layer. Allow them to sit undisturbed for a minute or two to develop a deep brown crust, then toss and repeat. Continue this process until the mushrooms are beautifully browned and any liquid they’ve released has evaporated. This browning intensifies their earthy flavor. Transfer to a bowl to cool.

STEP 4: Create Creamy Mashed Potatoes. Peel and evenly chop your Russet potatoes into approximately 2-inch chunks to ensure even cooking. Place them in a large pot, cover with cold water, and add a generous pinch of salt to the water. Bring to a boil, then reduce heat and simmer until the potatoes are fork-tender – a sharp knife inserted into a potato should slide in and out with no resistance, typically 15-20 minutes. Drain the potatoes thoroughly, then return them to the warm pot over very low heat for a minute or two to allow any remaining moisture to steam off. This step helps prevent watery mashed potatoes. Partially mash the potatoes, then add the butter, sour cream, milk, kosher salt, and black pepper. Continue mashing until they are smooth and creamy, without any lumps. Taste and adjust seasoning as needed. Allow the mashed potatoes to cool completely before assembly.

Tart Assembly: Bringing the Flavors Together

With all your delicious components prepped and cooled, it’s time for the exciting assembly phase, where your tart truly comes to life.

STEP 5: Prepare Your Crust Base. Preheat your oven to 375°F (190°C). Line a 10-inch cast iron skillet or a large baking sheet with parchment paper. Lightly flour a clean work surface, then roll out your chilled pie dough. Aim for a thickness of about ⅛ to ¼ inch, and a diameter large enough to cover your pan with a 2-3 inch overhang for folding. Carefully transfer the rolled dough into the prepared cast iron skillet or onto the parchment-lined sheet pan.

STEP 6: Layer the Rich Filling. To the center of the pie dough, spread the cooled mashed potatoes evenly, extending them to meet the edges of the cast iron pan, but leaving a 2-3 inch border of bare dough around the perimeter. Next, artfully dot the mashed potatoes with dollops of goat cheese. This ensures a delightful burst of tangy flavor in every bite. Follow this with an even layer of your browned mushrooms, then scatter the sweet caramelized onions over the top. Finally, sprinkle fresh thyme leaves generously over the entire filling, adding a fragrant, herbaceous touch.

STEP 7: Fold, Glaze, and Bake to Golden Perfection. Gently fold the excess pie dough edges towards the center, creating a beautiful rustic border. You may need to gently crease or pleat the dough in areas to ensure it folds neatly over the filling. In a small bowl, whisk together one egg with a small splash of water to create an egg wash. Using a pastry brush, generously brush the egg wash onto all exposed pie dough. This wash will give your crust that coveted golden-brown color and beautiful sheen. Bake in the preheated 375°F (190°C) oven for 45-55 minutes, or until the pastry is a rich golden brown and the filling is bubbly and heated through. Once baked, remove the tart from the oven and let it cool on a wire rack for about 15 minutes. This cooling period allows the tart to set, making for cleaner slices. Slice into wedges and serve warm!

Storing and Freezing Your Savory Tart

To enjoy leftover slices of this delicious potato and onion tart, store it covered tightly in the fridge for 3-5 days. For reheating, individual slices can be warmed in the microwave, or for a crispier crust, reheat the entire tart or slices in a 350°F (175°C) oven until the mashed potato layer is warm and the crust regains some of its crunch. Please note, this tart is not recommended for freezing, as the texture of the mashed potato filling may become compromised upon thawing and reheating.

Frequently Asked Questions & Expert Tips

Can I use store-bought pie dough for this recipe?

While convenient, we strongly advise against using store-bought pie dough for this particular tart. Our homemade all-butter pie crust recipe yields a much larger piece of dough when rolled out, which is essential to adequately contain the generous and delicious volume of filling. Store-bought doughs are typically smaller and thinner, making them prone to tearing or insufficient coverage for all the hearty ingredients.

What if I don’t have a tart pan?

Happily, a specialized tart pan is not required for this recipe! This rustic tart is designed to be forgiving and versatile. You can bake it in a 10-inch cast iron skillet, which imparts a wonderful crust, or simply on a large baking sheet lined with parchment paper for a beautiful free-form galette style.

Tips for Success:

• Patience with Caramelized Onions: The most crucial step for flavor development is the slow caramelization of onions. Keep the heat consistently low and stir occasionally. If they start to stick or brown too rapidly, add a tablespoon of water to deglaze and lower the heat. This process takes time but is incredibly rewarding.
• Dry Sautéing Mushrooms: For perfectly browned, flavorful mushrooms, ensure your pan is very hot and don’t overcrowd it. Cook in batches if necessary. Allow them to cook undisturbed for a minute or two before stirring, letting them develop that desirable golden crust.
• Cool All Components: Ensure the caramelized onions, browned mushrooms, and mashed potatoes are completely cool before assembling the tart. Adding warm fillings to cold pastry can melt the butter in the crust, leading to a less flaky result.
• Even Potato Chunks: When boiling potatoes, chop them into uniform pieces (around 2 inches). This ensures they cook evenly, preventing some from being undercooked while others become mushy.
• Seasoning is Key: Don’t forget to liberally salt the potato boiling water, and season your mashed potatoes to taste. The overall tart benefits from well-seasoned individual components.
• Adjust Goat Cheese: The amount of goat cheese can be adjusted to your preference. For a milder tang, use less; for a bolder flavor, feel free to add more.
• Serving Suggestions: This tart is fantastic on its own for lunch or a light dinner. It also makes an excellent side dish for roasted chicken or pork. For an appetizer, cut it into smaller squares. A simple green salad with a vinaigrette pairs beautifully with its richness.

More Savory Recipes to Try

If you loved this savory tart, be sure to explore more delightful recipes that hit all the right notes:

• Spinach and Feta Pinwheels: A delightful, bite-sized appetizer.
• Crab Pretzel: A unique and flavorful seafood twist.
• Prosciutto Asparagus Puff Pastry Bundles: Elegant and easy-to-make.

Did you create this delicious recipe? We’d love to see it! Share your photos on Instagram or Facebook and don’t forget to leave a star rating below to let us know what you think! For more culinary inspiration, be sure to follow us on Pinterest.

📖 Recipe

Mushroom, Caramelized Onion and Potato Tart

By Callan Wenner

This savory Mushroom, Caramelized Onion, and Mashed Potato Tart features a flaky pie crust filled with creamy mashed potatoes, tangy goat cheese, golden brown mushrooms, and sweet caramelized onions. Baked and topped with fresh thyme, this rustic pie is perfect as a meal, side, or appetizer.

Prep Time: 30 mins
Cook Time: 45 mins
Total Time: 1 hr 15 mins

Course: Appetizer, Main Course, Side Dish
Cuisine: American, French

Servings: 12
Calories: 165 kcal

Equipment

• Rolling Pin
• 10″ cast iron skillet or large baking sheet
• Pastry brush for egg wash

Ingredients

• 1 disc pie dough (using this all-butter pie crust)
• 2 large yellow onions, peeled and thinly sliced
• ½ tablespoon extra virgin olive oil (for onions)
• 2 russet potatoes, peeled and evenly chopped
• 2 tablespoons salted butter (28g)
• ¼ cup sour cream (57g)
• 2 tablespoons milk (30ml)
• ½ teaspoon kosher salt (for potatoes)
• ¼ teaspoon black pepper (for potatoes)
• 8 oz mushrooms of choice, quartered or roughly chopped
• 1 tablespoon olive oil (for mushrooms)
• 2-4 oz goat cheese
• 2 sprigs fresh thyme
• 1 egg (for egg wash)

Instructions

Pie Dough

1. Make the all-butter pie crust following recipe instructions and hydrate in the fridge for 2 hours.

Caramelized Onions

1. Remove the onion peels and thinly slice each onion, discarding the root.
2. Heat a large skillet over medium-high heat and add the olive oil. Then, add the sliced onions and toss to coat.
3. Reduce the heat to low and stir occasionally. The onions will begin to get translucent, then start to gain color, then turn to a nice caramelized color and texture.
4. Increase or decrease the heat, as needed, taking care not to burn the onions. This takes about an hour. Transfer to a bowl to cool.

Mushrooms

1. Clean and quarter the mushrooms. Then, heat a large pan over medium-high heat and let it get very hot. Add the olive oil and mushrooms and toss to coat, then spread them evenly in the pan.
2. Allow the mushrooms to cook for about a minute, then toss. Cook until browned and any liquid released has cooked off. Transfer to a bowl to cool.

Mashed Potatoes

1. Add water to a large pot and bring it to a boil. Peel and chop the potatoes into even pieces, about 2″ chunks.
2. Once boiling, salt the water liberally, then add the potatoes. Cook for 15-20 minutes, or until a sharp knife inserts into the center of the potatoes without any give.
3. Drain, then add back to the pot over low heat. Partially mash the potatoes, then add the butter, sour cream, milk, salt and pepper and continue mashing until smooth. Transfer to a bowl to cool.

Assembly

1. Preheat the oven to 375℉/190℃ and parchment line a cast iron pan or large cookie sheet.
2. Lightly flour your work surface and roll out the pie dough until it’s between ⅛-¼” thick, then drape it into the cast iron pan (or place on a sheet pan).
3. Spread the mashed potatoes evenly into the center (meeting the edges of the cast iron), leaving 2-3″ of the dough bare. Sprinkle the goat cheese on top of the mashed potatoes, followed by the mushrooms, caramelized onions, and thyme leaves.
4. Fold the excess pieces of pie dough in towards the center in 4-5 sections, gently pressing down.
5. Whisk together the egg and water, then brush it completely over the top of the pie dough.
6. Bake the tart for 45-55 minutes until the crust is golden in color. Remove from the oven and cool for about 15 minutes, then slice and enjoy!

Notes

Store the tart covered in the fridge for 3-5 days. Reheat in the microwave or a 350℉ oven until the potatoes are warmed through.

I do not suggest using store-bought pie dough for this. The homemade dough produces a larger crust, which is necessary to hold all of the ingredients.

Caramelized onions: be patient with this process and keep the heat relatively low. If the onions begin to burn at all, lower the heat and add in a tablespoon of water. Stir occasionally, but not too often.

Use your fingers to pull apart the caramelized onions to spread them evenly on top of the tart.

Nutritional Information (Estimate per serving)

• Calories: 165 kcal
• Carbohydrates: 16g
• Protein: 4g
• Fat: 10g
• Saturated Fat: 4g
• Polyunsaturated Fat: 1g
• Monounsaturated Fat: 4g
• Trans Fat: 1g
• Cholesterol: 24mg
• Sodium: 198mg
• Potassium: 267mg
• Fiber: 1g
• Sugar: 2g
• Vitamin A: 170IU
• Vitamin C: 4mg
• Calcium: 30mg
• Iron: 1mg

The provided nutritional information is an estimate per serving. Accuracy is not guaranteed.