Place cut pastry sheets onto a lined oven tray, and bake for approx. 7-10 minutes. Keep checking while you are cooking the pie in the next step to make sure it doesn't burn!
Cook pie filling
Heat a drizzle of oil in a large fry pan.
Cook mushrooms until softened (approx. 3 minutes).
Add the minced garlic, herbs, and corn flour to the pan. Stir while cooking for 1-2 minutes.
(Remember to check on the pastry in the oven!)
Add the water and cook until the sauce starts to thicken (approx 3-4 minutes).
Remove from the heat and stir through pesto and sour cream.
Serve
Serve the pie filling topped with a cooked pastry sheet.