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 until just combined. Roll into 1-inch balls and place on a tray.
03 - Heat a large skillet over medium-high heat with a splash of olive oil. Brown meatballs in batches for 5-6 minutes, turning to color all sides. They do not need to be fully cooked. Set aside.
04 - Bring a large pot of salted water to a boil. Cook pasta until al dente, 2 minutes less than package instructions. Drain and set aside.
05 - In the same skillet, heat 2 tablespoons olive oil over medium heat. Sauté onion until soft, about 5 minutes. Add garlic and cook for 1 minute. Stir in crushed tomatoes, tomato paste, dried basil, chili flakes, sugar, salt, and pepper. Simmer for 10 minutes until slightly thickened.
06 - Toss drained pasta with half the tomato sauce and transfer to the prepared baking dish. Arrange browned meatballs over the pasta, then pour remaining sauce over the top.
07 - Sprinkle mozzarella and Parmesan cheese evenly over the top.
08 - Bake for 25-30 minutes until golden and bubbly. Let rest for 5 minutes before serving. Garnish with fresh basil if desired.