Introduction
Caramelized Onion Tart delivers bakery-level results at home: sweet, slow-cooked onions on flaky puff pastry with thyme and Gruyère—simple, elegant, and crowd-pleasing.
Q: Is this beginner-friendly?
A: Yes. With low-and-slow onions and store-bought puff pastry, it’s very approachable.
Ingredients
- 2 large yellow onions, thinly sliced (Vidalia or shallots also work)
- 2 tbsp unsalted butter (or olive oil, or a 50/50 mix)
- 1 tsp fresh thyme leaves, finely chopped (or 1/2 tsp dried)
- Kosher salt & freshly ground black pepper
- 1 sheet puff pastry, thawed
- 1/2 cup Gruyère, shredded (Swiss or sharp white cheddar as alternatives)
- 1 egg, beaten (for egg wash)
Q: Butter or oil for onions?
A: Butter adds richness; a butter–oil mix raises the smoke point for longer cooking.
Substitutions
- Onions: Sweet onions for extra sweetness; shallots for delicate flavor.
- Herbs: Swap thyme for 1/2 tsp finely chopped rosemary.
- Pastry: Pie crust works, but puff pastry gives the signature flaky lift.
- Cheese: Try goat cheese for tang or cheddar for bolder bite.
Q: Any special handling for puff pastry?
A: Keep it cold and work quickly. See King Arthur Baking’s guidance.
Prep & Cook Time
Prep: 20 minutes • Cook: 30 minutes • Total: 50 minutes (≈15% faster than making pastry from scratch).
How to Make Caramelized Onion Tart
Step 1 — Caramelize the onions
Melt butter over medium-low heat. Add onions and a pinch of salt. Cook 20–25 minutes, stirring occasionally, until deep golden and very soft. Deglaze with a splash of water if fond builds up. Great technique primer: Serious Eats.
Step 2 — Prepare the puff pastry
Heat oven to 400°F/200°C. Unroll pastry on a parchment-lined sheet. Score a 1-inch border without cutting through; this helps edges puff.
Step 3 — Assemble
Spread onions inside the border. Sprinkle thyme and Gruyère. Brush edges with egg wash.
Step 4 — Bake
Bake 25–30 minutes until pastry is puffed and golden and cheese is bubbly. Rest 5 minutes before slicing.
Q: Edges browning too fast?
A: Tent loosely with foil and move the tray to a lower rack.
Nutritional Information (Estimate)
Per serving (~1/8 tart): 280–320 kcal • Protein 9–12 g • Fat 20–24 g (Sat 10–12 g) • Carbs 18–22 g • Fiber 2–3 g • Sodium 300–350 mg.
Healthy Alternatives
- Use olive oil and reduce cheese by 25% for a lighter tart.
- Dairy-free: plant-based cheese + olive oil.
- Gluten-free: certified GF puff pastry.
- Add thinly sliced mushrooms for extra veg.
Q: Can I reduce the fat?
A: Yes—use 1 tbsp butter + 1 tbsp olive oil and a lighter hand with cheese.
Serving Suggestions
- Pair with Green Goddess Salad for freshness.
- Serve alongside Creamy Mushroom Risotto for a cozy menu.
- Party board: add Roasted Red Pepper Hummus and Savory Herb Focaccia.
Common Mistakes & Fixes
- Rushing onions: high heat leads to bitterness—keep heat low and deglaze as needed (technique guide).
- Overworking pastry: handle minimally and keep it cold; see puff-pastry tips.
- Not scoring border: score ~1 inch in to help the rim rise evenly.
Storage & Make-Ahead
Refrigerate leftovers in airtight containers for up to 3 days; reheat at 350°F/175°C for 10–15 minutes to re-crisp. For food-safety basics (cooling and refrigeration within 2 hours), see the University of Maine Extension.
Q: Freeze it?
A: Baked puff pastry softens after freezing; better to freeze the assembled, unbaked tart and bake from frozen.
FAQ
Q: Best onions?
A: Yellow for balance; sweet for extra sweetness; shallots for delicate flavor. For nutrition data, check USDA FoodData Central.
Q: Prevent soggy bottom?
A: Fully preheat, use parchment, and bake on a lower rack for part of the time so the base gets direct heat.
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