01 - Heat olive oil in a large skillet over medium heat. Add ground beef and Italian sausage, breaking up the meat with a spoon. Cook until browned, about 6 to 8 minutes. Drain excess fat if necessary.
02 - Add onion, carrots, and celery to the skillet. Cook, stirring occasionally, until softened, about 5 minutes. Stir in garlic and cook for an additional minute.
03 - Transfer the meat and vegetable mixture to the slow cooker. Add crushed tomatoes, tomato paste, dry red wine, broth, oregano, basil, thyme, bay leaf, salt, black pepper, and red pepper flakes if using. Stir well to combine.
04 - Cover and cook on LOW for 8 hours or on HIGH for 4 hours, stirring once or twice during cooking if possible.
05 - Remove and discard the bay leaf. Stir in the milk or cream, then adjust seasoning to taste.
06 - Ladle hot sauce over cooked pasta. Garnish with fresh parsley and grated Parmesan cheese.