Savory Onion and Mushroom Tarts with a Flaky Crust

1Preheat your oven to 400°F (200°C).

2Roll out the puff pastry on a lightly floured surface to fit your tart pan. Place the pastry in the pan and trim the edges. Prick the bottom with a fork to prevent bubbling.

3In a large skillet, heat a tablespoon of oil over medium heat. Add the sliced onions (2 medium) and cook until they are soft and caramelized, about 15-20 minutes, stirring occasionally.

4Add the sliced mushrooms and minced garlic (2 cloves) to the skillet. Cook for an additional 5-7 minutes until the mushrooms are tender and any liquid has evaporated.

5Stir in the fresh thyme (1 tablespoon), balsamic vinegar (1 tablespoon), salt, and pepper. Remove from heat and let the mixture cool slightly.

6Spread the onion and mushroom mixture evenly over the puff pastry base. Sprinkle the grated Gruyère cheese (1 cup) on top.

7Brush the edges of the pastry with the beaten egg (1) to give it a golden color when baked.

8Bake in the preheated oven for 25-30 minutes, or until the pastry is golden brown and puffed up.

9Remove from the oven and let it cool for a few minutes before slicing. Serve warm or at room temperature.