Preheat the oven to 400º F (200C) and line a baking sheet with parchment paper.
Unfold puff pastry and use a rolling pin to roll it out a bit to make it wider.
Cut the dough into 6 pieces.
Divide grated cheese. Top with mushroom mixture and caramelized onion.
Brush the edges with beaten egg and fold the dough over the filling.
Use a fork to press the edges together to seal.
Transfer the hand pies to the prepared baking sheet.
Brush with beaten egg and top with grated Parmesan cheese.
Bake for 15-20 minutes or until golden and crisp.
Serve alongside your favorite dipping sauce or salad. Enjoy!