Sauté the soffritto. Heat olive oil in a large skillet over medium heat. Add the onion, carrots, and celery. Cook for 6–8 minutes, until softened and lightly golden. Add the garlic and cook 1 minute more. Transfer to the slow cooker.
Brown the meat. In the same skillet, add the ground beef and pork. Break it up with a wooden spoon and cook until browned and no pink remains, about 8 minutes. Drain off most of the fat, leaving about 1 tablespoon for flavor.
Deglaze. Pour the red wine into the skillet with the meat and scrape up the browned bits from the bottom. Simmer for 2–3 minutes until reduced by half. Stir in the milk and simmer 2 minutes more. Transfer everything to the slow cooker.
Combine. Add the crushed tomatoes, tomato paste, beef broth, bay leaves, oregano, thyme, nutmeg, salt, pepper, and Parmesan rind (if using) to the slow cooker. Stir well.
Slow cook. Cover and cook on LOW for 6–8 hours or HIGH for 3–4 hours. Low and slow is best.
Finish. Remove the bay leaves and Parmesan rind. Taste and adjust seasoning. Serve over cooked pasta, topped with grated Parmesan and fresh herbs.