In a pan add half of your butter. Toss in chopped onion, and sautée until soft and onions translucent (about 5 minutes).
Add your celery, carrot, and mushroom and saute for at least 10 minutes. Add the rest of your butter, if necessary, and add in your garlic and saute for an additional 5 minutes, stirring constantly until the veggies are brown and fragrant. Add your cooked green beans (add these earlier if you are adding frozen or raw beans).
Preheat the oven to 400 degrees F (200 degrees C)
Add your tablespoon of flour and mix until flour is cooked and beginning browning which will take about 1-2 minutes. Add your stock and stir until a bit of gravy forms around the veggies
Add the rest of your leftover gravy and mix so that everything is combined.
Remember, you may not need to add flour and stock in step 4, if you have a lot of gravy leftover (at least 2 cups). The addition and extra flour and stock is not needed.
In the same pan add shredded cooked chicken or turkey and heat up and break up meat for about 2 minutes or less.
Add your cream and mix until the mixture is combined. Add a splash of chicken broth to thin your pie filling if necessary.
Pour your pie filling in one pie crust, I bake directly in the foil tin the crust comes in. Cover your filling with the other crust. I let my second pie crust thaw completely, then roll it out slightly on a floured surface before using so the crust fits snuggly over the filling.
Seal the edges with your fingers.
Make an egg wash with one egg and 1 tablespoon of cream. Brush this over your pie.
Cut a small steam hole in the top crust or poke holes with a fork.
Bake in the preheated oven, on a baking pan, in case there is filling that bubbles over, for 30 to 35 minutes or until the crust is brown.
Remove from the oven when golden brown on top, let cool for 5-10 minutes and enjoy hot.