Slow-Caramelized Onion Tart with Thyme
A savory tart featuring deeply caramelized onions and fresh thyme, baked in a buttery crust for a sophisticated yet simple dish. This mediterranean-inspired vegetarian (gluten-free) ready in about 90 minutes layers medium, thinly sliced Yellow onion, Unsalted butter, All-purpose flour 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 8, 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
- 3 medium, thinly sliced Yellow onion
- 2 tbsp Unsalted butter
- 1 cup All-purpose flour
- 1/4 cup Cold water
- 2 tsp, plus more for garnish Fresh thyme leaves
- 1/2 cup Shaved Parmesan cheese
- 1 large Egg
Instructions
- Step 1: Preheat oven to 375°F (190°C). In a medium bowl, whisk 1 cup all-purpose flour, 1/4 teaspoon salt, and 2 teaspoons fresh thyme leaves. Cut in 2 tablespoons cold unsalted butter using a pastry cutter until mixture resembles coarse crumbs. Stir in 1/4 cup cold water until dough forms. Flatten into a disk, wrap in plastic, and chill for 30 minutes.
- Step 2: Roll chilled dough into a 12-inch circle on a floured surface. Transfer to a 9-inch tart pan, press gently into edges, and trim excess. Prick bottom with a fork. Bake blind for 15 minutes until golden. Remove parchment and weights.
- Step 3: While crust bakes, melt 2 tablespoons butter in a large skillet over medium-low heat. Add 3 thinly sliced yellow onions and cook slowly, stirring occasionally with a timer, for 30 minutes until deep golden brown and sweet — do not rush the caramelization.
- Step 4: Remove tart crust from oven. Spread caramelized onions evenly over base. Brush edges with beaten egg, then sprinkle 1/2 cup shaved Parmesan cheese over top. Bake for 12-15 minutes until cheese melts and edges are golden.
Frequently asked questions
How long does Slow-Caramelized Onion Tart with Thyme take to make?
Total time is about 90 minutes (45 min prep + 45 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 Slow-Caramelized Onion 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 Slow-Caramelized Onion 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 Slow-Caramelized Onion Tart with Thyme for a different number of people?
The recipe is written for 8 servings. Multiply each ingredient by (your serving target / 8). 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 Slow-Caramelized Onion Tart with Thyme gluten-free?
Yes — this recipe is tagged gluten-free based on its ingredient list. Always cross-check labels for packaged ingredients (sauces, broths, condiments) since formulations vary by brand.
What others are saying
- ★★★★★
This tart was a hit at my dinner party! The onions were perfectly caramelized and the thyme added a wonderful aroma.
- ★★★★☆
The tart was delicious, but I found the thyme a bit overpowering. Next time I'll use half the amount.
- ★★★☆☆
The onions took way longer than the recipe said, and the crust was too soggy. Not worth the time.
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