Caramelized Onion and Gruyère Tart with Thyme
A savory tart featuring sweet caramelized onions and nutty Gruyère cheese, accented with fresh thyme on a flaky puff pastry crust. This french-inspired vegetarian ready in about 55 minutes layers large, thinly sliced yellow onions, unsalted butter, olive oil 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 320 calories and feeds 6, 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.
Ingredients
- 1 sheet (9x12 inches), thawed puff pastry sheet
- 3 large, thinly sliced yellow onions
- 3 tbsp unsalted butter
- 1 tbsp olive oil
- 2 tsp fresh thyme leaves
- 1 1/2 cups shredded Gruyère cheese
- 1 tsp salt
- 1/2 tsp black pepper
- 1, beaten for egg wash egg
Instructions
- Step 1: Preheat oven to 400°F. In a large skillet, heat 3 tbsp unsalted butter and 1 tbsp olive oil over medium heat. Add 3 thinly sliced yellow onions and 1 tsp salt; cook, stirring frequently, for 25-30 minutes until onions are deeply golden and caramelized.
- Step 2: Stir in 2 tsp fresh thyme leaves and 1/2 tsp black pepper, cooking for 1 more minute until fragrant. Remove from heat and let cool slightly.
- Step 3: Roll out 1 thawed puff pastry sheet on a baking sheet lined with parchment paper. Score a 1-inch border around the edges, then prick the inner area with a fork to prevent puffing.
- Step 4: Spread the caramelized onion mixture evenly inside the border, then sprinkle 1 1/2 cups shredded Gruyère cheese over the top.
- Step 5: Brush the edges with 1 beaten egg for a golden finish. Bake for 20-25 minutes until puff pastry is golden brown and cheese is melted and bubbly.
- Step 6: Remove from oven, let cool for 5 minutes, then cut into squares and serve warm.
Equipment for this recipe
Top-rated tools to make this recipe successfully.
Frequently asked questions
How long does Caramelized Onion and Gruyère Tart with Thyme take to make?
Total time is about 55 minutes (15 min prep + 40 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 Caramelized Onion and Gruyère Tart with 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 Caramelized Onion and Gruyère Tart with 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 Caramelized Onion and Gruyère Tart with Thyme for a different number of people?
The recipe is written for 6 servings. Multiply each ingredient by (your serving target / 6). 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.
What goes well with Caramelized Onion and Gruyère Tart with Thyme?
French vegetarian like this pair well with a simple grain (rice, couscous, or crusty bread), a quick salad with acid (lemon vinaigrette, pickled onions), and a pan sauce or yogurt-based dip. Tap "Plan a meal with the AI" to get specific side suggestions.
