Ingredients: flour, for work surface, 1 sheet frozen puff pastry, 5 1/2 ounces (2 cups) Gruyere cheese, shredded, 1 egg, 1 1/2 pounds medium or thick green asparagus, 1 tablespoon olive oil, salt and pepper, 1 lemon, sesame seeds
- Preheat oven to 400 degrees. On a floured surface, roll the puff pastry into a 16-by-10-inch rectangle. Trim uneven edges. Place pastry on a baking sheet. With a sharp knife, lightly score pastry dough 1 inch in from the edges to mark a rectangle. Using a fork, pierce dough inside the markings at 1/2-inch intervals. Smear the sides of dough with egg yolk. Bake until golden, about 10 minutes.
- Remove pastry shell from oven, and sprinkle with Gruyere. Trim the bottoms of the asparagus spears to fit crosswise inside the tart shell; arrange in a single layer over Gruyere, alternating ends and tips. Brush with oil, and season with salt and pepper. Place on top lemon slices and toss some sesame seeds as well. Bake until spears are tender, 20 to 25 minutes. You can replace Gruyere cheese with 200 ml sour cream mixed with one egg yolk.