If you use fresh or frozen pastry shells, cook them according to the package instructions. Let them cool completely.
In a food processor, add the cooked ham, cream cheese, and Parmesan cheese.
Blitz until you get a creamy mousse consistency.
Season with salt and black pepper to taste.
Press the center of the vol-au-vent to create more space inside the shells. Make sure to not break the bottom.
With a piping bag or a spoon, fill each pastry shell and decorate with parsley. Serve immediately.
Notes
The mousse can be prepared up to 2 days in advance. Store it in an airtight container in the fridge, and fill the vol-au-vent shells just before serving.