Preheat oven to 200°C and line 2 baking trays with paper.
Sprinkle a little flour on a silpat mat and roll out the pastry into a rectangle. Using a large round cutter, cut out as many circles as you can get from the pastry. Using a cutter that is 1 cm smaller in diameter than the other one, cut circles from the middle of 1/2 of the rounds you have already cut, leaving you with rings of pastry. Set the inner circles aside and make smaller vol au vent with them.
Place the large rounds onto a lined baking tray and lay the 'rings' on top. Brush with egg wash. Grate some parmesan cheese on top. Bake for 15-20 minutes until puffed and golden. Timing will depend slightly on the size you make them as well as the accuracy of your oven. When they are cooked, remove from the oven and they can either be filled immediately or used later after cooling. They will stay crisp and be perfect for at least 24 hours as long as you are not in a humid climate.