Warm olive oil and butter in a large heavy pot over medium heat.
Cook pancetta until the fat renders and edges crisp, about 5 minutes.
Stir in onion, carrot, and celery with a pinch of salt. Soften until sweet, 7–8 minutes.
Add garlic and tomato paste. Cook, stirring, until paste darkens slightly, 2 minutes.
Crumble in beef and pork. Season with 1 tsp salt and pepper, then brown, 8–10 minutes.
Pour in red wine. Scrape the pot and simmer until mostly reduced, 3–4 minutes.
Stir in crushed tomatoes, milk, broth, oregano, nutmeg, sugar, and remaining salt.
Bring to a gentle bubble. Partially cover and simmer 90 minutes, stirring now and then.
Uncover and cook 30 minutes more to thicken. Adjust seasoning to taste.
Boil pappardelle in salted water until al dente. Reserve 1/2 cup pasta water; drain.
Toss pasta with enough sauce to coat, loosening with pasta water as needed.
Finish with Parmesan and parsley. Serve extra sauce and cheese at the table.