01 - Preheat oven to 400°F. Grease a 9x13 inch baking dish with cooking spray or olive oil.
02 - In a large bowl, combine ground beef, Italian sausage, breadcrumbs, Parmesan, egg, garlic, parsley, oregano, salt, and pepper. 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 boil. Cook pasta until al dente, 2 minutes less than package directions. Drain and set aside.
05 - In the same skillet, heat 2 tbsp olive oil. Sauté onion until soft, about 5 minutes. Add garlic and cook 1 minute. Stir in crushed tomatoes, tomato paste, basil, chili flakes, sugar, salt, and pepper. Simmer 10 minutes until slightly thickened.
06 - Toss drained pasta with half the tomato sauce and transfer to prepared baking dish. Arrange browned meatballs over pasta, then pour remaining sauce over top.
07 - Sprinkle mozzarella and Parmesan cheese evenly over the top.
08 - Bake for 25-30 minutes until golden and bubbling. Let rest 5 minutes before serving. Garnish with fresh basil if desired.