Start by melting the salted butter in a large skillet over medium heat. Add the halved onion to the pan and sauté until translucent and fragrant, about 5 minutes. If using, sprinkle in the dried chili flakes to add a touch of heat.
Pour in the 2400 grams of chopped tomatoes, stirring well to combine. Season with salt and pepper to taste. Let the sauce simmer gently while you prepare the meatballs, allowing the flavors to meld beautifully.
In a mixing bowl, combine the beef mince, dried oregano, tomato paste, egg, grated Parmesan or Pecorino, breadcrumbs, seedless raisins, chopped parsley, and crushed garlic. Sprinkle with a pinch of salt and pepper. Mix everything together until well combined, but be careful not to overwork the meat.
Using your hands, shape the mixture into meatballs about the size of a golf ball. You should get around 12-15 meatballs from this mixture. If desired, you can place them on a baking tray for easier handling.
Once your sauce has simmered for about 10 minutes, gently add the meatballs to the skillet. Cover and cook for about 20-25 minutes, turning occasionally, until the meatballs are cooked through and the sauce is thickened.
Meanwhile, bring a large pot of salted water to a boil. Cook the spaghetti according to package instructions until al dente. Drain and set aside.
Once the meatballs are cooked, add the drained spaghetti to the skillet, tossing gently to coat the noodles in the rich sauce. Serve immediately, garnished with additional Parmesan cheese and a sprinkle of fresh parsley.