Step 1: Preheat your oven to 375°F (190°C). Lightly grease a 9-inch deep-dish pie plate. Roll out one pie crust and carefully place it into the prepared pie plate, pressing it gently against the bottom and sides. If desired, you can pre-bake this crust for 10-15 minutes to help prevent a soggy bottom, then let it cool slightly.
Step 2: In a large skillet or Dutch oven, heat the olive oil over medium-high heat. Add the ground beef, breaking it apart with a spoon. Cook until browned, then drain off any excess fat. Transfer the beef to a bowl.
Step 3: Add the bulk Italian sausage to the same skillet. Cook, breaking it apart, until it’s fully browned. Drain any excess fat thoroughly.
Step 4: Reduce the heat to medium. Add the finely diced onion to the skillet and cook until softened, about 5-7 minutes. Stir in the minced garlic and cook for another minute until fragrant.
Step 5: Stir in the crushed tomatoes, tomato paste, dried oregano, dried basil, and red pepper flakes (if using) into the skillet with the onions and garlic. Add the water or beef broth. Bring the mixture to a simmer, then reduce heat to low and let it cook for 10-15 minutes, allowing the flavors to meld and the sauce to thicken. Season with salt and freshly ground black pepper to taste.
Step 6: Return the cooked ground beef and Italian sausage to the skillet with the sauce. Mix well to combine everything evenly. Let the mixture cool slightly before assembling the pie.
Step 7: Sprinkle half of the shredded mozzarella and provolone cheeses evenly over the bottom pie crust.
Step 8: Spoon the entire meat and sauce mixture over the cheese in the pie plate, spreading it evenly.
Step 9: Arrange about half of the sliced pepperoni over the meat mixture. Sprinkle the remaining mozzarella and provolone cheeses over the pepperoni.
Step 10: Roll out the second pie crust and carefully place it over the filling. Trim the edges of both crusts, leaving about a 1/2-inch overhang. Crimp the edges together to seal the pie. You can do this by hand or with a fork. Cut several slits in the top crust to allow steam to escape during baking.
Step 11: In a small bowl, whisk the large egg. Brush the top of the pie crust with the beaten egg wash. Sprinkle with grated Parmesan cheese if desired.
Step 12: Place the pie on a baking sheet (to catch any potential drips) and bake for 35-45 minutes, or until the crust is golden brown and the filling is bubbly. If the crust starts browning too quickly, you can loosely tent it with aluminum foil.
Step 13: Once baked, remove the pie from the oven and let it rest for at least 15-20 minutes before slicing and serving. This resting time allows the filling to set, making it much easier to cut neat slices.