Preheat the oven to 200°C.
Prepare the puffed pastry on a baking sheet.
Layer the Gruyère cheese and asparagus on top of the pastry.
Brush the pastry with egg wash.
Drizzle balsamic glaze over the asparagus.
Optional: Sprinkle Parmesan cheese on top.
Bake for about 25-30 minutes until golden brown.
