Mushroom and Gruyère Tart with Fresh Thyme

By Lauren Mitchell, Test Kitchen Director · Reviewed by AislePrompt Editorial · Published 2026-08-01 · Updated 2026-08-01

A savory tart featuring sautéed mushrooms and melted Gruyère cheese accented with fragrant fresh thyme in a flaky pastry crust. This French-inspired vegetarian recipe, ready in about 45 minutes, layers frozen puff pastry, cremini mushrooms, unsalted butter into a dessert worth slowing down for — great for weekend baking, holiday tables, or any time you want a sweet payoff at the end of a meal. Each serving lands at about 380 calories and feeds 4, so it slots into a weekend bake or a special-occasion dessert tray. Tap "Plan a meal with the AI" below to drop this recipe into your week and send the ingredients straight to Instacart. Nutrition values are approximate, calculated from USDA FoodData Central (fdc.nal.usda.gov) — verify against ingredient labels for any health-driven dietary plan.

Prep: 15 min Cook: 30 min Serves 4 French cuisine 380 cal/serving

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Ingredients

1 sheet (about 8x8 inches), thawed frozen puff pastry
10 oz, sliced cremini mushrooms
2 tbsp unsalted butter
2 small, finely chopped shallots
2 cloves, minced garlic cloves
1 tbsp fresh thyme leaves
1 cup, grated Gruyère cheese
1/4 cup heavy cream
1 large, beaten egg
to taste salt
to taste black pepper

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Equipment for this recipe

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Instructions

Step 1: Preheat oven to 400°F (200°C). Roll out 1 thawed sheet frozen puff pastry on a floured surface into a 9-inch square and place on a baking sheet lined with parchment paper. Score a 1-inch border around the edges without cutting through.
Step 2: In a large skillet, melt 2 tbsp unsalted butter over medium heat. Add 2 finely chopped shallots and sauté for 2 minutes until translucent.
Step 3: Add 10 oz sliced cremini mushrooms and 2 minced garlic cloves. Cook, stirring occasionally, for 6-8 minutes until mushrooms release moisture and become golden brown. Stir in 1 tbsp fresh thyme leaves, salt, and black pepper to taste.
Step 4: Remove mushroom mixture from heat and let cool slightly. Spread evenly within the scored border on the puff pastry.
Step 5: Sprinkle 1 cup grated Gruyère cheese evenly over the mushroom mixture.
Step 6: In a small bowl, whisk 1 large beaten egg with 1/4 cup heavy cream. Pour this over the tart filling to bind.
Step 7: Brush the exposed 1-inch pastry border with reserved beaten egg to ensure a golden crust.
Step 8: Bake tart for 20-25 minutes until the pastry is puffed and golden and the cheese is melted and bubbling.
Step 9: Let tart cool for 5 minutes before slicing and serving warm.

Frequently asked questions

How long does Mushroom and Gruyère Tart with Fresh Thyme take to make?

Total time is about 45 minutes (15 min prep + 30 min cook). Most home bakers find this fits a weekend afternoon; chill or store as the recipe directs before serving.

How do I store leftover Mushroom and Gruyère Tart with Fresh Thyme?

Cool fully before storing. Most baked desserts keep at room temperature in an airtight container for 2–3 days, or in the fridge for up to 5 days. Cream- or custard-based desserts must go in the fridge within 2 hours; reheat gently or serve cold per the recipe.

Can I substitute ingredients in Mushroom and Gruyère Tart with Fresh Thyme?

Yes — most ingredients in this recipe have flexible swaps. For oil, use any neutral high-smoke-point oil (avocado, grapeseed, refined coconut). For aromatics, dried herbs at ⅓ the volume of fresh work in a pinch. The full ingredient list is shoppable on Instacart so you can see substitutes in real time.

How do I scale Mushroom and Gruyère Tart with Fresh Thyme for a different number of people?

The recipe is written for 4 servings. Multiply each ingredient by (your serving target / 4). Cook time stays roughly the same up to 2x; for 3-4x batches, switch from a skillet to a sheet pan or stockpot so the food isn't crowded — overcrowding steams instead of browns.

Is Mushroom and Gruyère Tart with Fresh Thyme vegetarian?

Yes — this recipe is tagged vegetarian based on its ingredient list. Always cross-check labels for packaged ingredients (sauces, broths, condiments) since formulations vary by brand.