A French Onion Mushroom Tart combines the richness of caramelized onions, earthy mushrooms, and melted Gruyere cheese in a flaky puff pastry crust. This savory delight is perfect as an appetizer, snack, or light dinner.

Why You’ll Love This Recipe

Rich, Complex Flavors: Caramelized onions and Gruyere create a luxurious combination.
Easy Elegance: Simple to make yet looks and tastes gourmet.
Versatile Dish: Serve it as a starter, side dish, or even a main course.

Ingredients

(Tip: You can find the complete list of ingredients and their measurements in the recipe card below.)

3 tablespoons ghee or butter (divided)
2 medium onions, halved and thinly sliced
Salt and black pepper, to taste
¼ cup sherry (or white wine)
¼ cup beef stock
12 ounces shiitake or cremini mushrooms (or a combination)
2 cloves garlic, minced
1 tablespoon fresh thyme leaves (divided)
1 (14-ounce) package all-butter puff pastry, thawed
1 ¼ cups Gruyere cheese, grated
1 large egg, whisked (for egg wash)

Directions

Step 1: Caramelize the Onions

Heat 1 ½ tablespoons of ghee or butter in a large skillet over medium-high heat.
Add sliced onions with a pinch of salt and pepper. Cook, stirring occasionally, until golden and caramelized, about 20 minutes.
Deglaze the skillet with sherry and beef stock, stirring to incorporate. Transfer the onions to a bowl and set aside.

Step 2: Sauté the Mushrooms

In the same skillet, heat the remaining ghee or butter.
Add sliced mushrooms, salt, pepper, minced garlic, and half of the thyme.
Cook until the mushrooms are golden brown and fragrant. Remove from heat and set aside.

Step 3: Prepare the Puff Pastry

Preheat the oven to 400°F. Roll out the puff pastry onto a floured surface.
Place the pastry on a parchment-lined baking sheet.
Score a 1-inch border around the edges to create a crust. Be careful not to cut through the pastry completely.

Step 4: Assemble the Tart

Sprinkle half of the grated Gruyere cheese over the center of the pastry.
Layer the caramelized onions and sautéed mushrooms over the cheese.
Top with the remaining Gruyere cheese and sprinkle with thyme.

Step 5: Bake the Tart

Brush the pastry border with the whisked egg for a golden finish.
Bake for 26-30 minutes, or until the pastry is puffed and golden brown.
Allow the tart to cool slightly before slicing. Garnish with extra thyme leaves and serve warm.

Servings and Timing

Yield: 8 slices
Prep Time: 20 minutes (excluding puff pastry thawing)
Cooking Time: 50 minutes
Total Time: 1 hour 10 minutes

Variations

Cheese Options: Substitute Gruyere with fontina, Swiss, or a mix of Parmesan and mozzarella.
Vegetable Additions: Add spinach or roasted red peppers for extra flavor.
Herbs: Try rosemary or sage instead of thyme for a different aromatic profile.

Storage and Reheating

Storage: Store leftovers in an airtight container in the refrigerator for up to 3 days.
Reheating: Warm in a 350°F oven for 5-10 minutes to maintain the crispiness of the puff pastry.

FAQs

1. Can I make this tart in advance?

Yes, assemble the tart and refrigerate it (unbaked) for up to 12 hours. Bake fresh when ready to serve.

2. What if I don’t have Gruyere cheese?

You can use Swiss cheese or sharp cheddar as substitutes.

3. Can I use a different type of mushroom?

Absolutely! Cremini, button, or even portobello mushrooms work well.

4. Can I make this tart gluten-free?

Yes, use gluten-free puff pastry and check your stock and sherry for gluten-free certifications.

5. How do I keep the puff pastry from getting soggy?

Avoid overloading the tart with wet ingredients and bake immediately after assembly.

6. Can I use store-bought caramelized onions?

Yes, store-bought caramelized onions can save time, but homemade offers fresher flavor.

7. Can I freeze the tart?

Freeze the baked tart in individual portions. Reheat directly from frozen in a 375°F oven.

8. What can I serve with this tart?

Pair it with a simple green salad or a bowl of soup for a complete meal.

9. Can I add meat to this tart?

Yes, crumbled bacon or shredded chicken would complement the flavors.

10. Is it okay to use pre-sliced mushrooms?

Yes, but freshly sliced mushrooms provide better texture and flavor.

Conclusion

French Onion Mushroom Tart is an elegant yet straightforward dish that packs incredible flavor in every bite. With its flaky crust, rich toppings, and gooey melted cheese, it’s bound to become a favorite for gatherings or cozy nights in. Try it today and enjoy a slice of savory perfection!