Place a heavy-bottomed 6-quart saucepan or Dutch oven over medium heat and add the butter.
Add the diced red onion and cook, stirring occasionally, until softened about 5–8 minutes; reduce heat to medium-low if the onions begin to brown.
Stir in the minced garlic and sauté for about 2 minutes until fragrant.
Add the ground Italian sausage, ground beef, and dried oregano (or Italian seasoning). Cook, breaking the meat into small pieces, until well browned.
Pour in the tomato sauce and crushed tomatoes, stir to combine, then bring the sauce to a gentle simmer.
Cover and simmer the sauce for 30–60 minutes, stirring occasionally; 30 minutes is sufficient but you may simmer longer for deeper flavor.
Stir in the chopped fresh basil, then taste and season with salt and pepper as needed; if the sauce tastes too acidic, stir in 1–2 tablespoons sugar to balance.
Serve the meat sauce warm over cooked pasta.
