In a skillet heat butter and cook onions and celery about 3-5 minutes until tender.
Sprinkle in your flour and cook for 1 minute.
Add broth and heavy cream gradually and keep stirring as sauce thickens. This could take 3-5 minutes. As it thickens add in your mixed vegetables, salt, pepper, and seasonings. Set aside.
Put your pie crust into your pie pans or cast iron skillet. This amount of filling is perfect for a 12-inch cast iron skillet or would fit in 2 9-inch pie pans.
Fill with your chicken pot pie filling.
Cover with a top crust and cut slits in it to allow steam to vent out.
Bake at 375°F for 45-50 minutes.
Remove and let cool 10 minutes before serving. Sauce will thicken as it cools.