Prepare Potatoes: Bring potato cubes to a boil in salted water. Simmer for 15 minutes or until tender. Drain well and mash.
Cook Meat Mixture: While potatoes are cooking, brown ground beef, pork, onion, and garlic until no pink remains, using a spoon to break it up. Add remaining ingredients (including mashed potatoes) except for pie crust and bread crumbs. Bring to a boil, reduce heat, and simmer for 15 minutes or until thickened. Add 1 tablespoon of breadcrumbs if needed to help the mixture hold together. Cool for 20 minutes.
Preheat Oven: Preheat oven to 425°F.
Assemble and Bake Pie:
Line a deep-dish pie plate with the dough.
Add the meat pie filling.
Add the top crust and seal edges with a fork or your fingers.
Add a few slits to allow steam to escape.
Optionally, whisk 1 egg with 1 tablespoon of water and brush the egg wash over the crust.
Bake: Bake for 45-55 minutes or until bubbly and the crust is golden.