In a large pot, melt the butter with the olive oil. Add the pancetta and cook until it renders its fat. Add the chopped onion, carrot, and celery and sauté over medium heat for about 10 minutes until the vegetables are soft.
Increase the heat and add the minced meat. Brown it until cooked through and broken into small pieces. Pour in the wine and cook until it has almost completely evaporated.
Add the milk and let it be absorbed by the meat. Then, add the tomatoes, salt, and pepper. Reduce the heat to a minimum, cover, and let it simmer slowly for at least 2 hours. Stir the sauce occasionally.
Meanwhile, cook the tagliatelle in a large pot of salted boiling water until al dente. Drain them and serve immediately with the sauce and a generous amount of grated Parmesan.