Step 1

Preheat oven to 400 degrees F.

Step 2

Drizzle the asparagus spears with olive oil and a squeeze of lemon, then sprinkle with salt and pepper.

Step 3

Cut a piece of parchment paper to fit a baking sheet.

Step 4

Place the puff pastry on the parchment paper.

Step 5

Use a rolling pin and, moving from corner to corner diagonally, roll out puff pastry into an 11-inch x 14-inch rectangle.

Step 6

Score, without cutting all the way through, a 1-inch border all the way around.

Step 7

Prick the center rectangle with a fork but leave the 1-inch border alone.

Step 8

Brush with the mustard.

Step 9

Sprinkle Gruyere over the pastry. Don't put anything in the border area.

Step 10

Arrange the asparagus over the cheese, placing the spears close together.

Step 11

Sprinkle with Parmesan cheese.

Step 12

Bake for 20-25 minutes or until the crust is golden brown and puffy.

Step 13

Remove from the oven.

Step 14

Grate lemon zest over the top.

Step 15

Slice into squares to serve.