If you love the rich, soul-warming flavors of classic French onion soup and the earthy depth of mushrooms, this French Onion Mushroom Tart is about to become your new favorite savory bake. Elegant yet comforting, this tart combines deeply caramelized onions, golden sautéed mushrooms, nutty Gruyère cheese, and a flaky pastry crust into a dish that feels both rustic and refined.

Perfect for brunch, lunch, holiday appetizers, or even a cozy meatless dinner, this tart brings restaurant-level flavor to your home kitchen — without complicated techniques. The magic lies in patience: slow-cooked onions that transform into sweet, jammy perfection and mushrooms browned until their umami shines.

This recipe is designed to be approachable for home cooks while delivering bold, layered flavor. Whether you’re hosting guests or treating yourself to something special, this tart checks every box.

Why You’ll Love This French Onion Mushroom Tart

This isn’t just another savory tart — it’s a celebration of classic French flavors with a modern, versatile twist.

Deeply caramelized onions create natural sweetness without added sugar
Mushrooms add umami richness, making the tart hearty and satisfying
Gruyère cheese melts beautifully, delivering nutty, savory depth
Flaky crust provides contrast to the soft, creamy filling
Perfect hot or at room temperature, making it ideal for entertaining

It’s also vegetarian-friendly and endlessly adaptable, making it a staple recipe you’ll return to again and again.

Ingredients

For the Tart Crust

All-purpose flour
Cold unsalted butter, cubed
Salt
Ice-cold water

For the Filling

Yellow onions, thinly sliced
Cremini or button mushrooms, sliced
Olive oil
Unsalted butter
Garlic, minced
Fresh thyme leaves
Salt
Black pepper
Heavy cream
Eggs
Gruyère cheese, shredded

Instructions

Prepare the Tart Dough
In a mixing bowl, combine flour and salt. Cut in cold butter until the mixture resembles coarse crumbs. Add ice-cold water gradually, mixing just until the dough comes together. Form into a disc, wrap, and refrigerate for at least 30 minutes.
Caramelize the Onions
Heat olive oil and butter in a wide skillet over medium-low heat. Add sliced onions with a pinch of salt. Cook slowly, stirring occasionally, for 30–40 minutes until deeply golden and caramelized. Remove from heat and set aside.
Cook the Mushrooms
In the same skillet, add a bit more butter if needed. Sauté mushrooms over medium-high heat until browned and their moisture has evaporated. Add garlic and thyme, cooking briefly until fragrant. Season with salt and pepper.
Prepare the Filling Base
In a bowl, whisk together eggs and heavy cream until smooth. Stir in shredded Gruyère cheese.
Assemble the Tart
Roll out chilled dough and press into a tart pan. Spread caramelized onions evenly over the crust, followed by mushrooms. Pour the egg-cheese mixture over the top.
Bake
Bake at 375°F (190°C) for 35–40 minutes, or until the filling is set and lightly golden.
Cool and Serve
Let the tart rest for 10–15 minutes before slicing. Garnish with fresh thyme and serve warm or at room temperature.

Pro Tips for Perfect Results

Low and slow onions are essential — rushing them sacrifices flavor
Brown mushrooms properly by avoiding overcrowding the pan
Use freshly grated cheese for better melting and flavor
Let the tart rest before slicing to ensure clean cuts

Variations and Add-Ins

Add sherry or white wine to deglaze onions
Swap Gruyère for Comté or Swiss
Add goat cheese crumbles for tang
Include spinach or leeks for added vegetables

Serving Suggestions

Pair with a simple green salad and vinaigrette
Serve alongside soup for a cozy lunch
Cut into small squares for holiday appetizers
Enjoy with white wine or sparkling water

Cultural Inspiration

French onion flavors date back centuries, born from humble ingredients elevated through technique. This tart borrows that tradition and transforms it into a modern, versatile dish perfect for today’s tables.

Make-Ahead and Storage

Make dough up to 3 days ahead
Store baked tart in the fridge for up to 3 days
Reheat gently in the oven for best texture

Final Thoughts

This French Onion Mushroom Tart proves that simple ingredients, treated with care, can create something extraordinary. Rich, savory, and endlessly adaptable, it’s a recipe you’ll proudly share — and crave often.

French Onion Mushroom Tart

A savory tart made with caramelized onions, sautéed mushrooms, Gruyère cheese, and a flaky pastry crust.

Print Recipe Pin Recipe

Prep Time 30

Cook Time 45

Total Time 1 15

Servings: 6 slices

Course: Dessert, Snack

Cuisine: American, Autumn

Calories: 320