Thaw the pastry sheets at room temperature for 1 hour.
Preheat oven to 400 degree F. In a small bowl mix egg yolk with 1 teaspoon water; set aside. Unfold the pastry sheets on a lightly floured surface. Roll gently to flatten creases (you should have a 10-inch square). Cut 1/2-inch strips from all 4 sides of each pastry sheet. Brush the edges of the pastry sheets with the egg mixture. Place the cut strips on top and along edges of the pastry sheets, gently pressing in place to form a raised rim; trim ends. Place pastries on 2 baking sheets. Prick the centers with a fork. Brush pastries with egg mixture. Bake, 1 sheet at a time, about 15 minutes or until puffed and golden brown. Cool on baking sheets on wire racks.
Meanwhile, in a large skillet bring 1 cup water and a dash salt to boiling. Add asparagus and cook, covered, for 1 minute. Drain. Rinse asparagus with cold water; drain well. Transfer the asparagus to a cutting board. Slice 3-inch pieces from the tips of asparagus; set aside. Cut remaining asparagus into 2-inch pieces.
In a large mixing bowl whisk the eggs, milk, snipped dill, salt, and pepper together until well combined. In the large skillet melt butter over medium heat. Add egg mixture to skillet. Cook over medium heat without stirring, until mixture begins to set on bottom and around edges. With a spatula or a large spoon, lift and fold the partially cooked egg mixture so that the uncooked portion flows underneath. Continue cooking over medium heat for 2 to 3 minutes or until the egg mixture is cooked but still glossy. Remove the scrambled egg mixture from heat; fold in 1/2 cup of the cheese.
Spoon egg mixture into baked pastry shells on baking sheets. Top with the 2-inch asparagus pieces, salmon, and remaining 1/2 cup cheese. Arrange asparagus tips over all. Return 1 baking sheet at a time to oven and bake 3 to 5 minutes or until cheese is melted and filling is heated through. Garnish with fresh dill sprigs. Makes 8 servings.