Caramelized Onion and Gruyère Tartlets

These Caramelized Onion and Gruyère Tartlets are flaky, buttery, and filled with deeply caramelized onions and rich, nutty Gruyère cheese. They are the perfect appetizer or snack, offering a balance of sweet and savory flavors with a crispy pastry crust. Serve them as an elegant starter for a French-inspired meal or a holiday gathering.

(Makes 12 Tartlets)

For the Caramelized Onions

2 large onions (thinly sliced)

2 tbsp unsalted butter

1 tbsp olive oil

1 tsp sugar (optional, to enhance caramelization)

½ tsp salt

¼ tsp black pepper

1 tsp balsamic vinegar (for extra depth, optional)

For the Tartlets

1 sheet puff pastry (thawed)

1 cup Gruyère cheese (grated)

1 egg (beaten, for egg wash)

1 tsp Dijon mustard (optional, for extra tang)

½ tsp fresh thyme leaves (for garnish)

Caramelize the Onions

Heat Butter and Oil:
- In a skillet over medium heat, melt butter and olive oil.
Cook the Onions:
- Add sliced onions, salt, and sugar, stirring occasionally.
- Cook for 25-30 minutes, until golden brown and caramelized.
Add Vinegar and Season:
- Stir in balsamic vinegar, cook for 2 minutes, then set aside.

Prepare the Tartlet Shells

Preheat the Oven:
- Set to 375°F (190°C).
Cut the Puff Pastry:
- Roll out the puff pastry and cut into 12 equal squares or circles.
- Place them into a muffin tin or on a lined baking sheet.
Brush with Dijon (Optional):
- Spread a thin layer of Dijon mustard on each pastry.

Assemble and Bake

Fill the Tartlets:
- Spoon caramelized onions into each pastry shell.
- Sprinkle with Gruyère cheese.
Brush with Egg Wash:
- Lightly brush the edges of the pastry with beaten egg for a golden crust.
Bake Until Golden:
- Bake for 15-18 minutes, until puffed and golden brown.

Garnish and Serve

Add Fresh Herbs:
- Sprinkle with fresh thyme for an aromatic finish.
Pair with a Side:
- Serve with a light salad or a glass of white wine.

Pro Tips

For Extra Crispiness: Pre-bake the puff pastry for 5 minutes before adding the filling.
Make Ahead: Caramelize the onions a day in advance for easy assembly.
Try a Different Cheese: Swap Gruyère for Brie, Comté, or aged cheddar.

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Caramelized Onion and Gruyère Tartlets