French Onion Tart: A Savory Delight with Caramelized Onions and Cheese

Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper to prevent sticking.
2. Prepare the Onions:
In a large skillet, melt butter over medium heat. Add the sliced onions and a pinch of salt.
Cook the onions, stirring occasionally, for 15-20 minutes, until they are caramelized and golden brown.
Add the beef stock and thyme, and cook until the liquid is mostly evaporated. Remove from heat and let cool slightly.
3. Prepare the Puff Pastry:
Roll out the puff pastry on a lightly floured surface to smooth out any creases.
Place it on the prepared baking sheet. Use a knife to lightly score a 1-inch border around the edges of the pastry (do not cut through the pastry).
4. Assemble the Tart:
Spread the caramelized onions evenly over the center of the puff pastry, leaving the border clean.
Sprinkle the grated Gruyère cheese over the onions.
5. Apply the Egg Wash:
Brush the egg wash over the border of the pastry to help it turn golden during baking.
6. Bake:
Bake the tart in the preheated oven for 20-25 minutes, or until the pastry is golden and puffed.
7. Serve:
Let the tart cool slightly before slicing and serving.
Serving and Storage Tips