01 - Preheat the oven to 375°F. Roll out the pie crust and press it into a 9-inch pie dish. Trim any overhang and flute the edges. Prick the bottom lightly with a fork to prevent puffing. Set aside.
02 - Heat the olive oil in a large skillet over medium heat. Add the ground beef and cook, breaking it apart with a spoon, until evenly browned and cooked through, approximately 5 to 7 minutes. Drain excess fat if needed.
03 - Add the diced onion and minced garlic to the skillet. Sauté until softened, about 3 minutes. Stir in the marinara sauce, dried oregano, salt, and pepper. Bring to a gentle simmer and cook for 5 minutes to blend the flavors. Remove from heat.
04 - In a medium mixing bowl, combine the ricotta cheese, egg, 1 cup of the mozzarella, Parmesan cheese, chopped basil, and red pepper flakes. Stir until smooth and well incorporated.
05 - Spread half of the meat sauce evenly across the bottom of the prepared crust. Dollop the ricotta mixture over the sauce and gently spread it into an even layer. Top with the remaining meat sauce, then sprinkle the remaining 1 cup of mozzarella over the surface.
06 - Loosely tent the pie with aluminum foil. Bake for 30 minutes, then remove the foil and continue baking for an additional 15 minutes until the cheese is golden and bubbling.
07 - Allow the pie to cool for 10 minutes before slicing to let the layers set. Serve warm, garnished with additional fresh basil if desired.