In a large skillet, cook beef and sausage over medium heat until browned and crumbly, about 6-8 minutes. Drain.
Transfer cooked meat to a 6- or 7-quart slow cooker. Add tomatoes, tomato paste, onion, garlic, oil, vinegar (or wine), basil, oregano, brown sugar, salt, pepper and crushed red pepper. Cover and cook on LOW for 6-8 hours or on HIGH for 3-4 hours. Taste and season with additional salt, pepper or sugar, if necessary.
Serve sauce with cooked pasta and garnish with Parmesan cheese and fresh herbs, if desired.
Notes
Store leftover spaghetti sauce in an airtight container in the refrigerator for 3-4 days or in the freezer for up to 3 months.