1sheet puff pastry, about 9-10 oz, defrosted, but kept in the refrigerator
2Tablespoonsdijon mustard optional
1bunch, about 8 oz fresh asparagus, trim the tough ends
3cups(12 oz or 340 g) shredded gruyere cheese
½cup(1.5 oz or 42 g) shredded parmesan cheese
1large egg for egg wash
Freshly ground black pepper and tarragon leaves for garnish
Instructions
Preheat oven to 400℉. Line a baking sheet with parchment paper.
On a lightly floured surface, roll puff pastry dough out into a 11-inch by 14-inch rectangle. Trim the edges to make a straight line if necessary. Transfer to the prepared baking sheet. Score the edges by running a sharp knife through the top layer of puff pastry. Leave a 1-inch border, like a picture frame, and do not cut all the way through the dough. Prick the dough with a fork (not the border/edge).
Keep the 1 inch border clear for assembly. Use a pastry brush or the back of a spoon to spread mustard over the dough. Sprinkle gruyere over the puff pastry. Place asparagus spears parallel to each other on top of the cheese. Top with parmesan cheese.
Add the egg wash. Whisk together egg with 1 tablespoon water. Use a pastry brush to brush edges of the tart. It’s okay if you don’t use the entire mixture.
Bake at 400℉ for 20 to 25 minutes or until the crust is golden brown and puffy. Cool slightly and cut into squares. Garnish with freshly ground pepper and tarragon before serving.
Notes
Puff pastry should be still cool before going in the oven. This guarantees flaky layers. If it got too warm during assembly, place the tart in the refrigerator for 15 minutes before baking.Store tart in an airtight container in the refrigerator for up to 3 days. The tart is best when eaten the same day it is baked.Freeze for up to 1 month. After the tart has cooled, flash freeze for an hour, then wrap in plastic wrap and aluminum foil.