Step 1

In a large skillet over high heat, brown the beef and sausage and season with 3/4 teaspoon salt. Brown the meat, breaking it into smaller pieces with your spoon until cooked through, 4 to 5 minutes. Transfer to the slow cooker.

Step 2

Add 2 teaspoons olive oil to the skillet. Add onions, celery and carrots and sauté on medium-low for about 3 to 4 minutes, until soft. Transfer to the slow cooker, add the crushed tomatoes, bay leaves, and Parmesan rind if using, cover and cook low 4 to 6 hours. (Any longer, the sauce will burn.)

Step 3

When the meat sauce is ready, discard bay leaves and rind and serve.