01 - Preheat the oven to 375°F. Roll out the pie crust and gently press it into a 9-inch pie dish. Trim any overhang and flute the edges decoratively. Prick the bottom lightly with a fork to prevent puffing. Set aside.
02 - Heat olive oil in a large skillet over medium heat. Add the ground beef and cook, breaking it apart with a wooden spoon, until fully browned and no pink remains, approximately 5 to 7 minutes. Drain any excess fat if needed.
03 - Add the diced onion and minced garlic to the skillet with the beef. Sauté until the onion is softened and translucent, about 3 minutes. Pour in the marinara sauce, dried oregano, salt, and pepper. Stir to combine and let the sauce simmer gently for 5 minutes. Remove from heat and set aside.
04 - In a medium mixing bowl, combine the ricotta cheese, egg, 1 cup of the mozzarella, Parmesan, chopped basil, and red pepper flakes. Stir until the mixture is smooth, creamy, and evenly blended.
05 - Spread half of the meat sauce evenly across the bottom of the prepared pie crust. Spoon the ricotta mixture over the sauce in dollops, then gently spread it into an even layer. Top with the remaining meat sauce, spreading it to cover the cheese filling. Finish by sprinkling the remaining 1 cup of mozzarella evenly over the top.
06 - Loosely tent the pie with aluminum foil. Bake on the center rack for 30 minutes. Carefully remove the foil and continue baking for an additional 15 minutes, or until the cheese is golden brown and bubbling.
07 - Remove from the oven and allow the pie to rest for 10 minutes before slicing. This resting period helps the layers set for cleaner portions. Serve warm, garnished with additional fresh basil if desired.