1. Get frozen choux pastry (flaky dough) from the store.
2. Cut it to 3-inch squares if it is not already this size.
3. Make a square with a knife at 1/4" inside the dough, but do not cup through.
4. Bake the dough according to package instructions and let it cool down.
5. When cooked the choux pastry will grow and you will be able to remove the inside square.
6. Do not throw it; it will be the lid of the vol-au-vent.
7. Heat some oil in a large skillet and saute the mushrooms and garlic.
8. Deglaze with the white wine and add the bechamel.
9. If you do not have pre-made bechamel, you can make it right in the pan with the mushrooms.
10. Simply add some butter and flour and cook stirring for 2-3 minutes.
11. Start adding slowly the cream and milk and stir to avoid clumps.
12. Incorporate the Parmesan into the mushroom sauce, season and add the parsley at the end and fill the shells cavities with it.
13. Let the sauce overflow a bit. Top each vol-au-vent with its lid and serve.