Creating Caramelized Onion Puff Pastry Bites is straightforward when you follow these easy steps:

1. Preheat the Oven: Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
2. Caramelize the Onions: In a skillet, melt 2 tablespoons of butter with the olive oil over medium heat. Add the sliced onions and a pinch of salt. Cook for about 15-20 minutes, stirring frequently, until golden brown and caramelized.
3. Add the Mushrooms: Once the onions are caramelized, add the chopped mushrooms. Cook for an additional 5-7 minutes until the mushrooms are tender and any liquid has evaporated. Season with pepper and set aside to cool slightly.
4. Prepare the Puff Pastry: On a lightly floured surface, roll out the puff pastry sheet to smooth out any creases. Cut it into squares or circles, depending on your preference.
5. Fill the Pastry: Place a small spoonful of the onion and mushroom mixture in the center of each pastry square. Sprinkle shredded Gruyere cheese on top of the filling.
6. Seal the Bites: Fold the pastry over the filling to create a triangle or pocket shape. Press the edges well to seal. Use a fork to crimp the edges for extra security and decoration.
7. Prepare Egg Wash: Beat an egg in a bowl and brush the egg wash over the tops of the pastry bites for a beautiful golden finish.
8. Bake: Place the prepared bites on the lined baking sheet and bake in the preheated oven for 15-20 minutes, or until the pastry is puffed and golden brown.
9. Garnish: Optional – Sprinkle fresh thyme leaves on top for an added touch of flavor and color once they come out of the oven.
10. Cool and Serve: Allow the bites to cool for a few minutes before serving.

These steps will lead you to create amazing Caramelized Onion Puff Pastry Bites that will have everyone asking for seconds!