Heat a Dutch oven over medium. Cook pancetta until fat renders, 7–10 minutes. Add ground beef, season with salt and pepper, and brown well. Remove meat and set aside.
In the same pot, sauté onion, carrot, celery, and anchovies with a pinch of salt until very soft, 12–15 minutes.
Return the meat to the pot. Pour in wine and deglaze, scraping up any brown bits. Once wine evaporates, add beef stock, half the milk, tomatoes, parmesan rind, and bay leaves. Bring to a boil.
Cover tightly and transfer to a 300°F oven. Cook 2½ hours, stirring halfway. Uncover and cook 30 minutes more.
Stir in remaining milk and cream. Simmer on the stovetop for 15–30 minutes. Adjust seasoning to taste.
Boil pappardelle in salted water until just under al dente. Reserve 1 cup pasta water.
Toss cooked pasta with 3 cups ragu and ½ cup pasta water over medium-low heat until pasta is well coated and al dente. Add a pinch of nutmeg.
Serve hot, topped with Parmigiano Reggiano.