Saute the meat and aromatics: Heat the oil, butter, and prosciutto in a large pot over medium-high heat, and saute until the prosciutto starts to crisp up, about 3 minutes. Add the onion, carrot, celery, and ½ teaspoon kosher salt, and saute until the onion is softened, about 4 minutes. Stir in the garlic and tomato paste and saute until the tomato paste darkens, about 2 minutes. Add the ground beef and pork, sprinkle with the 1 teaspoon salt and ½ teaspoon pepper, and saute until the meat just loses its pink color. Increase the heat to high, add the wine, and bring to a boil. Stir in the milk, tomatoes, bay leaves, and Parmesan rind, and bring to a simmer.
Slow cook the Bolognese sauce: Transfer the ingredients to the slow cooker, cover, and cook on low heat for 8-10 hours or high heat for 4-5 hours.
Serve: Discard the bay leaves and Parmesan rind. Toss 1 pound of cooked pasta with 1 cup of the Bolognese sauce, then pour 3 more cups on top of the pasta. Freeze the rest of the sauce in 1 quart containers for later use.
