Melt butter in a large heavy pot or dutch oven over medium-high heat, and add in the pancetta. Stir frequently until crispy.
Remove the pancetta and set aside, leaving the fat in the pan. Add onion, carrot, celery, garlic, tomato paste and 1 teaspoon of kosher salt.
Saute, stirring frequently, for about five minutes. If the onion or garlic starts to brown reduce heat. Cook until fairly soft, then add in the pancetta again.
Add the beef and pork about a third at a time, allowing most of the liquid to evaporate before incorporating more.
Cook, stirring frequently, until all the pink is gone from the meat, all the liquid is evaporated and you can feel brown bits starting to stick to the bottom of the pot.
Deglaze the pot with the cup of white wine, scraping up all the browned bits. Then lower the heat to medium-low so it doesn't start sticking again.
Add milk, broth, tomatoes, 1 teaspoon of kosher salt, a crack of freshly ground black pepper and bring to a boil. Crush the whole tomatoes against the side of the pot with a wooden spoon (or cut them up before adding them).
Reduce heat to as low as possible maintaining a very lazy simmer. Add bay leaves and parsley.
Simmer on low, half covered, for four hours, stirring occasionally.
Once the cook time is up, remove bay leaves.
If the sauce has not completely thickened yet, increase heat slightly and simmer another 15 to 30 minutes with the lid off.
Serve with pasta and a healthy dose of freshly grated parmigiano reggiano.