Caramelized Onion and Gruyère French Onion Tart

By , Test Kitchen Director · Reviewed by AislePrompt Editorial · ·

A savory tart featuring slowly caramelized onions and nutty Gruyère cheese baked in a buttery pastry crust. This french-inspired brunch ready in about 55 minutes layers medium, 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 350 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.

Prep: 15 min Cook: 40 min Serves 6 French cuisine 350 cal/serving
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Ingredients

Instructions

  1. Step 1: Heat 3 tbsp unsalted butter and 1 tbsp olive oil in a large skillet over medium-low heat. Add 3 thinly sliced medium yellow onions, 1 tsp fresh thyme leaves, 1/2 tsp salt, and 1/4 tsp black pepper. Cook, stirring occasionally, for 30-35 minutes until the onions are deeply golden and caramelized.
  2. Step 2: Preheat oven to 400°F. Roll out 1 sheet puff pastry on a baking sheet lined with parchment paper. Score a 1-inch border around the edges without cutting through.
  3. Step 3: Spread the caramelized onions evenly within the scored border. Sprinkle 1 cup shredded Gruyère cheese evenly over the onions.
  4. Step 4: Brush the 1 egg yolk lightly beaten over the pastry border to create a golden crust.
  5. Step 5: Bake the tart for 20-25 minutes until the pastry is puffed and golden and the cheese is melted and bubbly. Remove from oven and let cool 5 minutes before slicing and serving.

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Frequently asked questions

How long does Caramelized Onion and Gruyère French Onion Tart 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 French Onion Tart?

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 French Onion Tart?

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 French Onion Tart 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 French Onion Tart?

French brunch 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.

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