Preheat your oven to 425°F (220°C) and line a baking sheet with parchment paper.

Roll out the thawed puff pastry into a large rectangle, about ⅛ inch thick, and cut into 6 equal squares.

Toss the trimmed asparagus with olive oil, kosher salt, and freshly ground pepper until well coated.

Layer each pastry square with a slice of prosciutto, followed by 3-4 pieces of seasoned asparagus, and sprinkle with shredded Gruyere cheese.

Lift the opposite corners of each pastry square to encase the filling and seal the edges tightly.

Brush the tops of each pastry bundle with the egg wash using a pastry brush.

Bake in the preheated oven for 12-15 minutes until golden brown.

Let cool for a couple of minutes before serving warm.