Sauté the aromatics: In a skillet over medium heat, melt the butter. Add the onion and celery, cooking until softened, about 5 minutes.
Prepare the sauce: Sprinkle the flour over the sautéed vegetables and stir well. Gradually pour in the chicken broth, whisking to form a thick, creamy sauce.
Mix the filling: Combine the turkey, corn, green bean casserole, mashed potatoes, and the sauce in the pan on the stove. Stir gently until everything is well incorporated.
Roll out the crust: Roll out the pie crust and cut circles slightly larger than your muffin tin wells or ramekin tops. Line each well with a crust, leaving enough to fold over the top. I didn't use bottom pie crusts just topped them for quicker assembly.
Fill the pies: Spoon the turkey mixture into each crust-lined well. If desired, cut smaller circles of dough for tops and seal the edges with a fork. Use a knife to cut small vents in the tops for steam to escape.
Bake: Place the pot pies in the oven and bake for 20–25 minutes, or until the crust is golden brown and the filling is bubbling.