Cut onion, carrot, and celery in large chunks. Place into a food processor and pule until finely chopped. Set aside.
Heat oil in a large Dutch oven over medium heat. Once hot, add ground chuck to pan in chunks and a pinch of salt. Stir to cook, without breaking apart the beef, until the beef is browned, but not crispy, about 6 minutes. It's okay if the beef is still pink inside. It will finish cooking later. Drain beef and set aside. Wipe the inside of the Dutch oven to remove excess fat.
Cook pancetta in pot over medium heat (no need to add extra oil because the pancetta fat will render as it cooks), until the pancetta starts to turn crispy but doesn't burn, about 8 minutes. Add onion-celery-carrot mixture to the pan and cook until the mixture starts to stick to the pan, about 8 minutes.
Use wine to deglaze the pan and release browned pieces from the bottom of the pan. Add the beef and start breaking apart the beef into tiny pieces, using a wooden spoon. Cook until the wine is almost evaporated, about 12 minutes.
Add in tomato paste, bay leaf, and nutmeg. Cook for 5 minutes, making sure to press the paste into the beef and stir around. Pour in chicken broth and milk. Stir together. Reduce heat to the lowest setting on your smallest burner. You want it to be barely simmering.
Leave uncovered to cook for 2-2½ hours, or until a thick consitency in the sauce is reached. if this happens before 2 hours, add ½ cup more chicken broth so that sauce keeps cooking and developing it's flavor. Discard bay leaf when complete and keep heat on.
Set a large pot of salted water to boil and cook paste a little before al dente (2 minutes less than package instructions). Using tongs, transfer the pasta to the sauce pot with about 1 cup of pasta water and ½ cup of freshly grated Parmesan cheese. Stir together and bring to a simmer. Cook for 2 minutes. Give it a taste and add salt, if needed. Serve immediately.