Asparagus Tart

0 Preheat oven to 400 degrees F.
1 Drizzle the asparagus spears with olive oil and a squeeze of lemon, then sprinkle with salt and pepper.
2 Cut a piece of parchment paper to fit a baking sheet.
3 Place the puff pastry on the parchment paper.
4 Use a rolling pin and, moving from corner to corner diagonally, roll out puff pastry into an 11-inch x 14-inch rectangle.
5 Score, without cutting all the way through, a 1-inch border all the way around.
6 Prick the center rectangle with a fork but leave the 1-inch border alone.
7 Brush with the mustard.
8 Sprinkle Gruyere over the pastry. Don't put anything in the border area.
9 Arrange the asparagus over the cheese, placing the spears close together.
10 Sprinkle with Parmesan cheese.
11 Bake for 20-25 minutes or until the crust is golden brown and puffy.
12 Remove from the oven.
13 Grate lemon zest over the top.
14 Slice into squares to serve.