Easy Cheesy Caramelized Onion Tart with a Mashed Potato Crust
The first time I made this tart, the kitchen filled with the most intoxicating aroma. It was a cold Sunday afternoon, and I was faced with a sack of potatoes and a bag of onions, the humble beginnings of what I thought would be a simple supper. But as the onions slowly melted into a sweet, jammy tangle and the potatoes were whipped into a cloud of buttery goodness, an idea sparked. Why not use the mashed potatoes as the crust? The result was nothing short of magic. This Cheesy Caramelized Onion Tart with a Mashed Potato Crust is the ultimate comfort food fusion—a crispy, golden potato shell cradling a deeply savory, sweet, and cheesy filling. It’s a dish that feels both elegantly rustic and wonderfully indulgent, perfect for a cozy night in or a show-stopping centerpiece for guests.
Why You’ll Love This
Ultimate Comfort Food: It combines two of the most beloved comfort foods—creamy mashed potatoes and rich, cheesy tart—into one unforgettable dish.
Naturally Gluten-Free: The ingenious mashed potato crust means this impressive tart is effortlessly gluten-free, no special flours required.
A Labor of Love That’s Worth It: The slow, gentle caramelization of the onions is a therapeutic process that fills your home with an incredible fragrance and builds deep, complex flavor.
Unexpectedly Elegant: Despite its simple ingredients, the final result looks and tastes gourmet, making it perfect for holidays, potlucks, or date night.
An Unexpected Rave Review
I once served this at a family gathering where my uncle, a man whose culinary preferences are famously limited to “meat and potatoes,” eyed it with deep suspicion. He reluctantly took a small slice, then immediately went back for a second, much larger helping. He later confessed he thought it was some kind of “fancy quiche” and was shocked that the crust was made of potato. It’s now the only thing he requests I bring to every event, proving this tart has the power to win over even the most skeptical of eaters.
What Makes It Special
The Potato Crust: A genius, gluten-free alternative to pastry that is crispy on the outside, tender on the inside, and so full of buttery flavor.
Slow-Caramelized Onions: This isn’t a quick process. Cooking the onions low and slow for over an hour transforms their sharp, pungent flavor into a sweet, deeply savory, and melt-in-your-mouth jam.
The Cheese Duo: The combination of smoky, creamy Gouda and tangy, bright goat cheese creates a perfect balance of flavors that cuts through the richness of the onions and potato.
Making It Happen
This recipe is a journey of building layers of flavor. It begins with the onions. In your largest skillet, you’ll melt butter with olive oil and add a mountain of thinly sliced onions. They will seem like far too much, but trust the process. You’ll cover them and let them cook down slowly, stirring occasionally. After an hour, you’ll remove the lid and let them continue their transformation, becoming sticky, golden, and caramelized. A bit of minced garlic stirred in at the end adds its aromatic warmth.
While the onions work their magic, you’ll turn your attention to the potatoes. Boil them until completely fork-tender, then drain and mash them smoothly with milk, butter, and salt. This isn’t just a topping; this is your crust. You’ll press this warm, creamy mashed potato mixture into a tart pan, building up the sides to form a sturdy edge. This par-bakes in the oven until the bottom is set and the edges are just beginning to turn a beautiful golden brown.
Once the crust is ready, the fun assembly begins. You’ll gently press down the center of the crust with a spoon to create a well for the filling. Then, layer in half of your deeply flavorful onions, crumble over the delightful tang of goat cheese, and sprinkle a layer of that smoky Gouda. Repeat with the remaining onions and cheese, creating a beautiful, layered masterpiece. A final brief bake melts the cheese into a gooey, irresistible blanket. Letting it rest for a few minutes after baking is crucial—it allows everything to set so you can slice perfect, clean wedges.
You Must Know
Patience with Onions is Key: Do not rush the caramelization process. Medium-low heat for a long time is the secret to sweet, not burnt, onions.
Press the Crust Firmly: When forming your potato crust, press it firmly and evenly into the pan to prevent crumbling later.
Let it Rest: Allowing the tart to rest for 10-15 minutes after baking is non-negotiable. It allows the cheesy filling to set, making it possible to slice neatly.
Serving Ideas
Serve this stunning tart warm, cut into wedges. It is a hearty vegetarian main that pairs beautifully with a simple arugula salad dressed in a sharp lemon vinaigrette to cut through the richness. For a heartier meal, add a side of roasted asparagus or sautéed garlicky mushrooms. A crisp, dry white wine like Sauvignon Blanc or a light-bodied Pinot Noir would be excellent drink pairings.
Make It Different
Herbaceous Twist: Stir 2 tablespoons of fresh chopped thyme or chives into the mashed potato crust for an extra layer of flavor.
Bacon Lover’s Dream: Crisp up 6 slices of chopped bacon and sprinkle it over the onions before adding the cheese.
Dairy-Free/Vegan: Use vegan butter and milk in the potatoes, and substitute the cheeses with your favorite high-quality vegan alternatives that melt well.
Different Cheese: Swap the Gouda for sharp white cheddar or fontina, and the goat cheese for creamy blue cheese if you prefer a stronger flavor.
Storage and Reheating
Store any leftover tart in an airtight container in the refrigerator for up to 3 days. To reheat, place individual slices on a baking sheet and warm in a 350°F oven for 10-15 minutes until heated through. This method will help keep the crust crispy. Microwaving is not recommended as it will make the potato crust soft.
Success Tips
Use a non-stick skillet for the onions to prevent sticking and make cleanup easier.
Ensure your tart pan has a removable bottom—it is essential for getting the tart out in one beautiful piece.
For extra crispy edges on the potato crust, you can brush them lightly with a little melted butter before the initial bake.
Frequently Asked Questions (FAQ)
Can I make any parts of this tart ahead of time?
Absolutely! The onions can be caramelized up to 3 days in advance and stored in the fridge. The mashed potato crust can be prepared and pressed into the tart pan, covered, and refrigerated a day ahead. Let it come to room temperature for 20 minutes before baking.
My mashed potatoes are very wet. Will this work?
You want a fairly stiff mash, not a loose and creamy one. Be sure to drain your boiled potatoes very well and avoid adding too much liquid. The crust needs to be sturdy enough to hold its shape.
Can I use a different type of onion?
Yellow onions are ideal for their high sugar content and balanced flavor. You can use sweet onions (like Vidalia) for an even sweeter result, but avoid red onions as they will discolour the filling.
I don’t have a tart pan. What can I use instead?
A 9-inch springform pan will work in a pinch. Alternatively, you can press the potato mixture into a well-greased pie dish, though you will lose the fluted edge and may need to serve it from the dish.
Why do I need to push the center of the crust down after the first bake?
The potato crust will puff up slightly during baking. Pressing it down creates a deeper well for the generous amount of filling, ensuring you get a perfect cheese-to-crust ratio in every bite.
Cheesy Caramelized Onion Tart with a Mashed Potato Crust
A stunning vegetarian showstopper featuring a crispy, golden mashed potato crust filled with sweet caramelized onions, tangy goat cheese, and melted smoky gouda.
Prep Time: 30 minutes
Cook Time: 1 hour 45 minutes
Total Time: 2 hours 15 minutes (plus resting time)
Category: Main Course, Side Dish
Cuisine: American, Fusion
Difficulty: Intermediate
Yield: 8 servings
Ingredients
5 tablespoons unsalted butter, divided
2 tablespoons olive oil
4 large yellow onions, thinly sliced (about 12 cups)
2 garlic cloves, minced
1 teaspoon salt, divided
2 pounds golden potatoes (such as Yukon Gold), peeled and cut into chunks
1/3 cup milk (2% or whole)
2 cups shredded gouda cheese
4 ounces goat cheese, crumbled
Directions
Caramelize the Onions: In a large nonstick skillet, heat 2 tablespoons of butter and the olive oil over medium-low heat. Add the sliced onions, stir to coat, and cover. Cook for 1 hour, stirring every 10 minutes to prevent sticking.
Remove the lid and continue to cook for another 30 minutes, stirring every 10 minutes, until the onions are deeply golden brown and caramelized. Add the minced garlic and remaining 1/2 teaspoon of salt, cook for 1 minute more, then remove from heat.
Make the Potato Crust: While onions are cooking, place potato chunks in a large pot and cover with cold water. Bring to a boil over high heat and cook for 10-15 minutes, or until fork-tender. Drain thoroughly.
Return the drained potatoes to the pot or a large bowl. Mash until smooth. Add the milk, remaining 3 tablespoons of butter, and remaining 1/2 teaspoon of salt. Stir until well combined and creamy.
Par-Bake the Crust: Preheat oven to 350°F (175°C). Generously grease a 10-inch tart pan with a removable bottom.
Transfer the warm mashed potatoes to the prepared tart pan. Using your hands or a spoon, press the potatoes evenly into the bottom and up the sides to form a crust.
Bake for 40-45 minutes, or until the crust is set and the edges are lightly golden. Remove from oven and gently press down the center of the crust with the back of a spoon to create a well.
Assemble and Finish Baking: Evenly spread half of the caramelized onions over the bottom of the potato crust. Sprinkle the crumbled goat cheese over the onions, followed by 1 cup of the shredded gouda. Top with the remaining onions and finish with the remaining 1 cup of gouda.
Return the tart to the oven and bake for 5-7 minutes, or just until the cheese is fully melted and bubbly.
Rest and Serve: Let the tart rest in the pan on a wire rack for 10-15 minutes. Gently run a toothpick or thin knife around the edge to loosen, then carefully remove the outer ring of the tart pan. Slice into wedges and serve warm.
Notes
Allergy Info: This recipe is naturally gluten-free. Contains dairy.
Nutrition: Nutritional information is an estimate and may vary based on specific ingredients used. Approximate values per serving: Calories: 415, Fat: 25g, Saturated Fat: 14g, Carbohydrates: 32g, Fiber: 4g, Sugar: 8g, Protein: 16g.
