Golden French Onion Tart

Preheat the Oven – Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper.
Caramelize the Onions – In a large skillet, melt butter over medium heat. Add sliced onions and a pinch of salt. Cook for 15-20 minutes, stirring occasionally, until golden and caramelized.
Deglaze and Season – Add beef stock and thyme to the skillet, cooking until the liquid mostly evaporates. Remove from heat and let cool slightly.
Prepare the Puff Pastry – Roll out the puff pastry on a lightly floured surface to smooth any creases. Transfer to the prepared baking sheet. Lightly score a 1-inch border around the edges (without cutting through).
Assemble the Tart – Evenly spread the caramelized onions over the center of the pastry, leaving the border clean. Sprinkle with grated Gruyère cheese.
Egg Wash the Edges – Brush the border of the pastry with beaten egg.
Bake – Bake for 20-25 minutes, until the pastry is golden and puffed.
Cool and Serve – Let the tart cool slightly before slicing and serving.
Serving and Storage Tips