To prepare the oven, set the temperature to 400° and cover two large baking sheets with parchment paper. In a small bowl, mix the melted butter, honey, and salt together.
In a medium bowl, toss asparagus in oil.
Cut the puff pastry into 12 equal squares. To do this, first roll out each sheet of pastry on a surface dusted with flour until it forms a rectangle of 15 by 10 inches. Then cut each rectangle into 6 smaller squares.
Turn the square pastry 45 degrees to make a diamond shape and coat it with the butter mixture. Put a prosciutto slice on top, tucking in the edges to fit inside the diamond. Add some asparagus pieces and a brie slice on top of the prosciutto. Fold the left side of the pastry over the filling and brush it with egg wash. Then fold the right side over and apply more egg wash on the top and sides of the pastry. Sprinkle some pepper on top. Transfer the pastry to a baking sheet and repeat the same steps with the remaining pastry.
Bake until golden and brie is melted, about 15 minutes.
Brush with more butter mixture before serving.