If you are using stock, bring the stock to a boil. Add cornstarch to cold water, and blend until smooth; whisk into stock to thicken.
Line a 9 inch pie plate with pastry. Mix turkey and vegetables together, and place in pie crust. Pour gravy or thickened stock over turkey and vegetables. Cover with remaining pie crust. Cut slits in the top to release steam.
Place pot pie on a cookie sheet to prevent stock from over flowing into your oven. Cook in center of oven until crust is golden brown, approximately 1 hour. Slice, and serve hot.