Heat olive oil in a large heavy bottom pot over medium heat. Add onions, celery, carrot, and a pinch of salt. Sauté until translucent and soft but not browned, about 8 minutes.
Increase the heat to medium-high and add the beef, pork and pancetta. Season with salt and freshly ground pepper and break up with the back of a wooden spoon and cook until browned.
Add the wine and reduce heat to medium, cook down until the wine is almost completely evaporated.
Add the milk and cook down until almost completely evaporated. Stir in the ground nutmeg.
Add tomato paste and cook 2 to 3 minutes.
Add the tomatoes.
When it starts to bubble, turn the heat down to very low and cook uncovered for 2 to 3 hours. Stir every once in a while.* If the sauce gets dry at any point, add chicken stock, 1/2 cup at a time.
Once the liquid has reduced and sauce is thick; season well with salt & pepper, then set aside or refrigerate.
When ready to eat, add the sauce to a 12” skillet and warm through. Swirl in 3 tablespoons butter.
Cook the pasta al dente (reserving 1/2 cup of the water), then add it to the skillet with the sauce. Gently stir to combine and cook for about 3 more minutes with the sauce, adding reserved pasta water if is too thick.
Serve with plenty of freshly grated parmesa-reggiano cheese.
The Bolognese is best served with fresh pasta. You can make it at home with my Easy Homemade Pasta Dough recipe. After rolling the pasta dough out into sheets, you can make tagliatelle noodles by rolling each sheet up and cutting 1/2" noodles with a chef's knife. The Sauce is even better the next day, so make it a day ahead of time if you can.