To make the Italian soffritto, mix and pulse the onion, celery, and carrot in a food processor until very finely chopped, almost to a puree consistency then transfer to a small bowl.
Heat the extra-virgin olive oil in a large pot over medium heat. Break apart the beef into small clump size patties (about 1½") and add to the pot; season lightly with salt. Cook the meat turning occasionally until the beef is lightly browned on each side, but not crispy, 7–8 minutes per side. It may still be a little pink in the center but that’s okay. The meat will complete cooking throughout the rest of the process. Use a slotted spoon to transfer the beef to a medium bowl.
Remove any remaining meat pieces and the fat from the pan and wipe clean with a paper towel. Now take the pancetta and dice it into small cubed pieces (about ¼"), you can purchase sliced pancetta and dice it to desired size. Cook the pancetta in the pot over medium heat, stirring occasionally, until the pancetta has released some of its fat and is crisp, approximately 8 minutes. Add the soffritto (onion-carrot-celery mixture) to pot and cook, stirring occasionally, until vegetables are very soft and beginning to stick to the surface, 7–8 minutes.
Return the beef to pot and pour in the white wine. Reduce heat to medium-low and cook, smashing down on beef with a wooden spoon breaking it up into small pieces, until wine is evaporated, surface of pot is almost dry, and meat is finely ground, approximately 15 minutes. (The meat should be in little bits and pieces now) Add the tomato paste, bay leaf, and nutmeg and cook, stirring occasionally and still breaking down and pressing on meat, until the tomato paste is slightly darkened; about 5 minutes.
Pour the chicken stock and milk into pot; add a small pinch of salt. Reduce heat to the lowest setting and simmer uncovered, stirring occasionally, until meat is very, very tender, 2½ –3 hours. There should not be any rapid boiling or bubbles at this stage of the cooking process. Instead, the sauce should slowly cook and release the occasional small bubble or two as it simmers. When finished, the sauce should have the texture of and look like a sloppy joe mixture. If the liquid reduces before the meat is completely tender, add an extra ½-cup chicken stock and continue cooking. Remove the bay leaf. Taste sauce and adjust seasoning with salt as needed; keep warm.
Cook pasta in a large pot of lightly salted boiling water, minus 2 minutes per package directions, as it will finish cooking through the final 2 minutes in the sauce. Rustichella d’Abruzzo for around 4 min. Please note that if you are making a smaller portion for two people only, you will want to use half of the pasta package.
If you are making a smaller serving for only 2 people, add two cups of the meat sauce in a separate medium pan on low heat, and using tongs, transfer the pasta to pan with the meat sauce and mix. Add ½-cup of the pasta cooking water and a ½-cup of Parmesan cheese to the pan and mix thoroughly. Increase heat to medium and bring to a simmer. Continue cooking and tossing the pasta constantly, until pasta is al dente and sauce has slightly thickened, about 2 minutes. If making the full serving size, prepare the whole pasta package and use all the meat sauce. Transfer the pasta to the pot with meat sauce and follow the same process, instead adding 1-cup of the pasta cooking water.
Using your tongs, transfer the pasta to a serving platter and top with more Parmesan cheese.
If making only for two and you have remaining meat sauce you can store it in the refrigerator for 3 days or freeze the sauce for future use.