01 - Preheat your oven to 400°F. Grease a 9x13 inch baking dish with olive oil or cooking spray.
02 - In a large mixing bowl, combine ground beef, Italian sausage, breadcrumbs, Parmesan cheese, egg, minced garlic, parsley, oregano, salt, and black pepper. Mix until just combined—avoid overworking the meat.
03 - Roll the mixture into 1-inch balls, approximately 2 tablespoons each. Place on a baking sheet or tray.
04 - Heat a large skillet over medium-high heat with a splash of olive oil. Brown meatballs in batches for 5–6 minutes, turning to brown all sides. They need not be fully cooked through. Transfer to a plate and set aside.
05 - Bring a large pot of salted water to boil. Cook pasta until al dente, 2 minutes less than package directions. Drain well and set aside.
06 - In the same skillet, heat 2 tablespoons olive oil over medium heat. Sauté onion until soft and translucent, about 5 minutes. Add minced garlic and cook for 1 minute until fragrant. Stir in crushed tomatoes, tomato paste, dried basil, chili flakes, sugar, salt, and pepper. Simmer for 10 minutes until slightly thickened.
07 - Toss the drained pasta with half of the tomato sauce. Transfer to the prepared baking dish and spread evenly.
08 - Arrange browned meatballs over the sauced pasta. Pour the remaining sauce evenly over the meatballs and pasta.
09 - Sprinkle shredded mozzarella and grated Parmesan cheese evenly over the top.
10 - Bake for 25–30 minutes until cheese is melted and golden, and the sauce is bubbling around the edges. Let rest for 5 minutes before serving.
11 - Garnish with fresh basil leaves if desired. Serve hot with crusty bread and a green salad.