Heat olive oil in a large Dutch oven over medium-high heat. Add ground beef, ground pork, salt, and pepper. Cook until browned, about 10-12 minutes. Transfer meat to a paper towel-lined plate. Add pancetta/bacon to the pot and cook until crisp, 5-7 minutes. Transfer to the same plate.

Reduce heat to medium, add remaining olive oil. Add diced onion, carrots, and celery. Cook until soft and translucent, about 8 minutes. Add minced garlic and cook until fragrant, about 1 minute. Stir in tomato paste and cook for 2 minutes.

Stir in milk, tomatoes, bay leaves, thyme, and cheese rind (if using). Combine well. Return the cooked meats to the pot. Season with salt and pepper.

Bring sauce to a simmer, then partially cover and reduce heat to medium-low. Cook until thickened, about 1.5 to 2 hours, stirring occasionally.

Remove and discard bay leaves, thyme, and cheese rind.

Season to taste with more salt and pepper if needed. Serve hot over your favorite pasta, with grated cheese.