In a large Dutch oven, heat EVOO, 2 turns of the pot, over medium to medium-high heat. Add butter to oil and when it foams, add onions and soften 5 minutes. Add celery, carrots and garlic, stir a minute or 2 more to coat then add meat and season with salt and finely ground black pepper. Break up the meat and cook until it loses its pink color then add bay, parsley stems and milk. Season with a little freshly grated nutmeg and reduce heat to a simmer. Let milk absorb into meat completely then add wine and let that absorb. Stir tomatoes into the sauce and reduce heat to low.
Bring the stock or water to a simmer with a chunk of rind then reduce heat to low. When the sauce looks like it may be drying out, add a few ladles of the warm liquid to moisten it, keeping the Bolognese at a low bubble. Simmer sauce for 3-4 hours, adding liquid as necessary.
Before serving, remove bay leaf and parsley stems.
Cook pasta in 6 quarts boiling, salted water about a 1-1 1/2 minutes shy of al dente per package directions. Reserve half a mug full of starchy cooking water if you have used all of your stock or Parm-infused warm water. Drain pasta or remove it from the pot with a spider/strainer. Toss pasta with a few pats of butter and combine it with sauce and a little stock or the reserved water if necessary to loosen.
Serve with grated Parmigiano-Reggiano cheese at table.
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