Preheat the oven to 350 and melt the butter in a saucepan, cook the chopped onion until tender. Stir in celery and carrots and cook for a few minutes, then stir in herbes de provence (optional) and flour, cook for an additional 2 minutes. Add the stock and gravy (optional) and bring to a simmer. Add the potatoes and simmer until tender. Then, stir in the turkey, parsley and peas. Pour mixture into baking dish or 4 ramekins and top with optional stuffing and cranberry sauce.
Top the mixture with puff pastry (or pie crust), with edges hanging over the side and brush with egg wash. Bake for 20-30 minutes, until crust is golden.