Prepare the all-butter pie crust as directed, creating 2 dough disks and allow the dough to chill before rolling out.
Place an empty light metal cookie sheet in your oven and preheat it to 400 degrees
Roll 1 disk of dough out and press into a pie dish that has been sprayed with non-stick spray. Trim off the overhang edges with a sharp knife.
Scoop your leftovers in layers into the pie crust; 1 1/2 cup mashed potatoes on the bottom, topped with 1 cup stuffing, 1 cup chopped turkey, and then pour the 3/4 cup gravy on top.
Roll the second dough disk out and place it on top, trim the excess edges, then crimp the pie crust edges.
Whisk 1 egg and 1 tablespoon of water and brush it on the top crust with a pastry brush. Slice in ventilation slits in the middle of the pie.
Place the pie in the oven directly on the empty cookie sheet and bake for 40 minutes. Remove and allow the pie to cool down a bit before serving.
Notes
Note: Using the empty cookie sheet method will send direct heat to the bottom of the pie, ensuring the bottom crust is thoroughly baked and not soggy.