Melt butter in a large heavy pot or dutch oven over medium-high flame.
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.
Add pancetta and continue to cook, stirring frequently, until the vegetables are fairly soft.
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. Make sure you get up all those bits. Then lower the heat 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.
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.
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.