1. In a wide skillet, melt butter over medium-low heat.

2. Add sliced onions, salt, pepper, and thyme.

3. Cook slowly, stirring often, for 25–30 minutes, until golden and soft.

4. Add brown sugar (if using) and stir until dissolved.

5. Deglaze with wine or sherry, scraping up brown bits. Simmer for 2–3 minutes until the liquid reduces.

6. Optional: Stir in a splash of balsamic at the end for tangy-sweet complexity.

7. Let cool slightly before filling the tartlets.

If using puff pastry:

1. Preheat oven to 400°F (200°C).

2. Lightly flour a surface and roll out puff pastry to 1/8-inch thick.

3. Use a 2.5-inch cookie cutter to cut 24 rounds.

4. Press rounds into a mini muffin tin to form little cups.

5. Use a fork to gently prick the bottoms.

6. Optional: brush edges with egg wash for golden color.

1. Add a tiny dab of Dijon mustard to the bottom of each pastry shell (if using).

2. Spoon in a small amount of caramelized onion (about 1–2 tsp per tartlet).

3. Top with a generous pinch of grated Gruyère cheese.

1. Bake for 15–18 minutes, or until:

   • Pastry is puffed and golden

   • Cheese is melted and lightly browned

2. Cool in the pan for 5 minutes, then remove and serve warm.

• Caramelized onions: Up to 3 days in advance

• Assembled (unbaked) tartlets: Refrigerate for 1 day or freeze for longer

• Baked tartlets: Can be reheated at 350°F for 5–7 minutes

• Add a dot of fig jam or caramelized apples for a sweet contrast

• Use blue cheese or brie instead of Gruyère

• Try mini phyllo cups for a lighter version

• Add a little prosciutto or crisp pancetta to the filling

• Wine: Chablis, dry rosé, or a French Pinot Noir

• Cocktail: French 75, classic martini, or sparkling cider

• Non-alcoholic: Elderflower soda, iced lavender tea, or sparkling grape juice