French Onion Mushroom Tart (2024)

My French onion mushroom tart combines the rich, savory flavor of French onion soup and sauteed mushrooms in this divinely delicious appetizer. Prepared with store bought puff pastry, this hot, flaky tart is layered with jammy caramelized onions kissed with sherry, sautéed mushrooms sprinkled with garlic and thyme, plus nutty and creamy Gruyere cheese!

A Mushroom Tart with a French Onion Twist

Coming up with delectable appetizers to serve during the holiday season is one of my all-time favorite things to do when it comes to recipe developing.

I love being able to pack lots of irresistible flavor into small “packages” to enjoy with a little glass of wine as a simple snack, or to pass around to guests to whet their appetites and take the edge off a little before a bigger meal is to be served.

Crisp, hot, flaky tarts are among my favorite to prepare and serve, especially when they're brimming with creative ingredients that offer an abundance of flavor in little bite-fulls.

My French onion mushroom tart is my latest favorite to prepare, and I love to serve it on its own with a glass of wine for a date night in for my hubby and I, or pass it around to a small gathering as something to get our appetites going before enjoying dinner.

Prepared with good quality, store-bought puff pastry, layered with Gruyere cheese, caramelized onions, and sauteed mushrooms, my French onion mushroom tart recipe takes the flavor we love in French onion soup and combines it with mushrooms to create a tart with rich, earthy and incredibly savory flavors.

Bet you can't eat just one slice!

My Recipe for French Onion Mushroom Tart

Friends, just because an appetizer is loaded with lots of mouthwatering flavor, doesn't mean it has to be complicated to prepare.

Part of what I appreciate about this elegant little French onion mushroom tart is that with a few steps, we have a terrific offering to share, one that is memorable and totally crave-worthy.

Making use of good quality, store-bought puff pastry is the way to go here, so there's no need to make tart dough from scratch—a nice time saver!

The only stove-top cooking here is caramelizing the onions for the “French onion” portion of the recipe (I add a bit of sherry and beef stock to create the deep flavor), then saute the mushrooms with some garlic and a finish of fresh thyme leaves for added earthiness.

And if you really want to simplify things for yourself, then prepare the onions and the mushrooms a day or two beforehand, so those are ready to go.

All that's left the day you'd like to serve this is to thaw, roll, and top your puff pastry sheet, then bake your tart!

Here's a glance at my French onion mushroom tart recipe: (or just jump to the full recipe...)

1. To get started, I prepare my onions by cooking them down until deeply caramelized and golden, and set those aside to cool.
2. Next, I saute my mushrooms, and allow those to cool on a paper towel-lined plate to absorb excess moisture.
3. I then thaw my puff pastry sheet, gently roll just enough to even it out and make it symmetrical, then create a little border around the edges by gently scoring with a paring knife. I use a fork to prick the center of the puff pastry sheet to keep it from puffing too much during baking.
4. Then, I add my topping and bake the tart for 28 minutes, until deeply golden, puffed and flaky.
5. To finish, I sprinkle fresh thyme leaves over the French onion mushroom tart, cut into 8 pieces, and serve hot or room temp.

Recipe

French Onion Mushroom Tart

by Ingrid Beer

Print Recipe

This French onion mushroom tart is layered with caramelized onions kissed with sherry, tender sautéed mushrooms, plus creamy Gruyere cheese!

Category: Appetizer
Cuisine: French-American

Yield: Serves 8

Nutrition Info: 361 calories (per serving/slice)

Prep Time: 20 minutes (does not include thaw time for puff pastry)
Cook time: 50 minutes
Total time: 1 hour 10 minutes

Ingredients:

• 3 tablespoons ghee or butter, divided use
• 2 medium onions, halved and sliced thinly
• Salt
• Black pepper
• ¼ cup sherry (or white wine)
• ¼ cup beef stock
• 12 ounces shiitake or cremini mushrooms, or combo of both
• 2 cloves garlic
• 1 tablespoons fresh thyme leaves, divided use
• 1 (14 ounce) package all-butter puff pastry (1 large sheet), thawed according to package instructions
• 1 ¼ cups grated Gruyere cheese
• 1 whisked egg, for egg wash

Preparation:

1. Begin by gathering and prepping all of your ingredients (keeping the puff pastry cold) according to the ingredient list above to have ready and organized for use.
2. Place a large, heavy-bottom skillet over medium-high heat (cast iron is terrific for this), and add in 1 ½ tablespoons of the ghee or butter. Once melted, and the skillet is hot, add the sliced onions plus a sprinkle of salt and black pepper.
3. Cook the onions, stirring quite frequently, until cooked down and deeply caramelized and jammy, roughly 20 minutes. Once caramelized, pour in the sherry, and allow it to bubble up for a moment. Next, add in the beef stock, and allow it to bubble up.
4. Reduce the heat to low for a moment, and spoon the onions into a dish or bowl to hold and to cool.
5. To the same skillet, add the remaining 1 ½ tablespoons of ghee or butter and bring the heat back up under it to medium-high once more.
6. Add in the sliced mushrooms plus a sprinkle of salt and pepper, and saute the mushrooms for about 5 to 7 minutes, until golden but still meaty with some texture. Stir in the garlic and sprinkle in 1 teaspoon of the fresh thyme into the mushrooms. Once aromatic, turn off the heat.
7. Spoon the mushrooms into a separate bowl or dish lined with paper towel (to absorb excess moisture) to cool.
8. Preheat the oven to 400°.
9. To prepare the tart, place a piece of parchment paper the size of your baking sheet (I use an 18 by 13 inch baking sheet) in front of you on a work surface, and sprinkle lightly with flour. Place the thawed puff pastry sheet in front of you on the parchment, and give it a gentle roll with a rolling pin, just enough to even the edges and make it symmetrical. (You want a size that's roughly 10 x 13 inches, and ⅛” thick.)
10. Create a border for your tart by using a sharp knife to gently score the pastry about ½ inch from the edge, all the way around, taking care not to cut all the way through the pastry (you just want to make a light line with the your knife). Use a fork to prick the center of the puff pastry a few times (not the border) to help it to bake flat. (Place the pastry into the fridge to chill for a few minutes if it is becoming warm.)
11. Lightly sprinkle ¾ cup of the cheese on the bottom, then top with the sautéed mushrooms and the caramelized onions. Sprinkle over this another ½ cup of cheese.
12. Gently egg wash the border you created, and bake the tart for 26 to 30 minutes (mine took about 28 minutes), or until a deep, golden brown.
13. Allow the French onion mushroom tart to cool on the baking sheet for 10 minutes, then sprinkle over the remaining 2 teaspoons of the thyme leaves as garnish, and cut the tart into 8 pieces. Serve hot, or at room temp.

See Also

Tomato Spinach Frittata - Bake. Eat. Repeat.Basmati Rice Pilaf with Fruits and Nuts - The Vegan AtlasPepperoni Basil Tomato Puffs"Dominostein" Blechkuchen. Mmmhhh....!

Tips & Tidbits for my French Onion Mushroom Tart recipe:

• All-butter puff pastry: I like to use Dufour brand all-butter puff pastry for this recipe, and it can be found at Whole Foods Market as well as other stores. It's great quality, tastes delicious, and the 14 ounce package contains one larger sheet of puff pastry, rather than two smaller sheets found in other brands. You can use the two smaller sheets, if that's what you have on hand, just divide the topping ingredients in half to create two smaller tarts.
• Make ahead for ease: For convenience sake, I often like to prepare my caramelized onions and my sauteed mushrooms a day or two before I plan on serving these tarts, as it saves me time the day of. This way, they're both completely cool already (you can leave them at room temp for 30 minutes to take the chill off), and all you have to do is thaw and prep your puff pastry, top, and bake.
• Gruyere cheese for creamy, nutty flavor, or your favorite kind: Gruyere is the classic cheese that tops French onion soup, so it gives this French onion mushroom tart that distinct flavor. Good swap outs are mozzarella or provolone, asiago, even white cheddar or jack cheese.
• Reheating your French onion mushroom tart: We like to reheat our leftover slices of tart in our toaster oven at about 325° for about 5 minutes—it re-crisps and reheats really well!

Hungry for more cozy appetizers? Check out this Baked Brie with Caramelized Onions, this Cheese Ball, this Whipped Goat Cheese, this Savory Pear Tart, or this Artichoke Dip, or this Tomato Tart!