Heat the olive oil and butter in a large Dutch oven or heavy-bottomed pot over medium heat. Add the finely diced pancetta and cook, stirring occasionally, until crisp and golden brown, about 6-8 minutes. Remove the crisp pancetta with a slotted spoon and set aside, leaving the rendered fat in the pot.

Add the ground pork and ground beef to the pot. Increase the heat to medium-high and cook, breaking up the meat with a wooden spoon, until well browned and no longer pink. This can take 8-10 minutes. Drain off any excess fat from the pot, leaving about 1-2 tablespoons.

Reduce the heat to medium. Add the finely diced onion, carrots, and celery to the pot. Cook, stirring occasionally, until the vegetables have softened and become translucent, about 8-10 minutes. Add the minced garlic and cook for another 1 minute until fragrant.

Pour in the dry white wine, scraping the bottom of the pot with your wooden spoon to loosen any browned bits (fond). Bring to a simmer and cook until the wine has almost completely evaporated, about 5-7 minutes.

Stir in the whole milk. Bring it to a gentle simmer and cook until the milk has nearly evaporated and been absorbed by the meat and vegetables, about 10-15 minutes. This step is crucial for the sauce's creamy texture.

Add the beef (or chicken) broth, bay leaf, freshly grated nutmeg, salt, and black pepper. Stir to combine.

Bring the sauce to a bare simmer, then reduce the heat to very low. Cover the pot, leaving a slight crack for steam to escape, and simmer for at least 2.5 to 3 hours, or even longer (up to 4 hours), stirring every 30-45 minutes to prevent sticking and ensure even cooking. The longer it simmers, the more tender the meat will become and the more complex the flavors will develop. The sauce should be thick and rich. If it becomes too thick, you can add a little more broth or water.

Once the sauce has simmered sufficiently, remove the bay leaf. Stir in the reserved crisp pancetta and 1/2 cup of freshly grated Pecorino Romano or Parmigiano-Reggiano cheese. Taste and adjust seasoning if necessary.

Serve immediately over freshly cooked pasta (like tagliatelle or pappardelle), garnishing with additional grated cheese and a sprinkle of black pepper.