01 - Preheat oven to 400°F. Grease a 9x13 inch baking dish with cooking spray or olive oil.
02 - Combine ground beef, Italian sausage, breadcrumbs, Parmesan cheese, egg, minced garlic, parsley, oregano, salt, and pepper in a large bowl. Mix gently until just combined—avoid overworking the mixture.
03 - Roll mixture into 1-inch balls, approximately 24 meatballs. 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 sear all sides. They will finish cooking in the oven. Transfer to a plate and set aside.
05 - Bring a large pot of salted water to boil. Cook pasta for 2 minutes less than package directions for al dente texture. 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 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 drained pasta with half the tomato sauce. Spread evenly in prepared baking dish. Arrange browned meatballs over the pasta. Pour remaining sauce over the meatballs.
08 - Sprinkle shredded mozzarella and grated Parmesan cheese evenly over the top of the meatballs and pasta.
09 - Bake for 25–30 minutes until cheese is melted and bubbly with golden-brown spots. Remove from oven and let rest for 5 minutes before serving.
10 - Top with fresh basil leaves if desired. Serve warm alongside a green salad and crusty bread.