Begin by breaking up the whole tomatoes in a large bowl using your hands or a fork, creating a chunky texture. Set aside.

In a medium soup pot, heat olive oil and butter over medium heat. Add chopped onion and sauté for about 5 minutes until translucent. Stir in minced garlic and cook for 30 seconds.

Pour the prepared tomatoes into the pot, add Italian seasoning, oregano, sugar, and crushed red pepper flakes. Stir and bring to a boil. Reduce heat to low and simmer uncovered for 30 minutes.

Combine breadcrumbs and milk in a large mixing bowl until a paste forms. Add ground beef, pork (or sausage), egg, Parmesan cheese, and parsley. Mix gently and shape into 18 meatballs.

Place the meatballs into the simmering sauce. Let them simmer for 35-45 minutes, turning occasionally until fully cooked.

Taste the sauce and adjust seasoning with salt and pepper. Serve over spaghetti and garnish with more Parmesan cheese and basil.