Preheat the Oven
Preheat your oven to 375°F (190°C).
Cook the Meat Mixture
In a large skillet over medium heat, cook the ground beef, sausage, and onion until browned. Drain excess grease. Add garlic, Italian seasoning, salt, and pepper. Stir in the pizza sauce and let it simmer for 5 minutes.
Prepare the Pie Crust
Roll out one pie crust into a deep-dish pie plate, pressing it into the bottom and up the sides. Set aside the second crust for the top.
Assemble the Pie
Layer half the meat mixture into the crust. Sprinkle with half the mozzarella. Add a layer of pepperoni. Repeat with the remaining meat, cheese, and pepperoni. Top with cheddar cheese if using.
Seal the Pie
Place the second pie crust over the top. Trim any excess dough and crimp the edges to seal. Cut a few slits in the top to allow steam to escape. Brush with a beaten egg for a golden finish.
Bake
Bake for 35–45 minutes, or until the crust is golden brown and the filling is bubbly. If the edges brown too quickly, cover them with foil halfway through baking.
Cool & Serve
Let the pie rest for 10–15 minutes before slicing — this helps the filling set for clean, hearty slices.