01 - Preheat your oven to 400°F. Grease a 9x13 inch baking dish with cooking spray or a thin layer of olive oil.
02 - In a large mixing bowl, combine ground beef, Italian sausage, breadcrumbs, Parmesan cheese, egg, minced garlic, parsley, oregano, salt, and black pepper. Mix gently until just combined—do not overwork. Shape the mixture into 1-inch balls and arrange on a baking sheet or tray.
03 - Heat a large skillet over medium-high heat with a splash of olive oil. Add meatballs in batches, being careful not to overcrowd the pan. Brown for 5–6 minutes, turning to sear all sides evenly. They will finish cooking in the oven, so they do not need to be cooked through. Transfer browned meatballs to a plate and set aside.
04 - Bring a large pot of salted water to a boil. Add pasta and cook until al dente, about 2 minutes less than the package instructions. Drain thoroughly in a colander and set aside.
05 - In the same skillet used for meatballs, heat 2 tablespoons olive oil over medium heat. Add chopped onion and sauté until softened, 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. Reduce heat to low and simmer for 10 minutes, stirring occasionally, until slightly thickened.
06 - Toss the cooked pasta with half of the tomato sauce until evenly coated. Transfer the sauced pasta to the prepared baking dish. Arrange the browned meatballs evenly over the pasta, then pour the remaining sauce over the top.
07 - Sprinkle shredded mozzarella and grated Parmesan cheese evenly across the entire surface, covering the meatballs and pasta.
08 - Bake at 400°F for 25–30 minutes, until the cheese is melted and golden brown, and the sauce is bubbling around the edges. Remove from oven and let rest for 5 minutes before serving. Garnish with fresh basil leaves if desired.