Heat butter and oil, over medium-high heat, in a heavy-bottomed pot that can later snugly accommodate the pork.
When the butter foam subsides, put in the roast fat-side down.
Brown the meat evenly on all sides.
If the fat is becoming very dark, reduce the heat.
Season the roast with salt and pepper; add the milk slowly to prevent from boiling over; add the nutmeg.
Bring to a boil; reduce the heat to a simmer; set the lid slightly ajar.
Cook slowly for about 2-1/2 to 3 hours, occasionally turning and basting the meat.
If before the meat is fully cooked, the liquid in the pot has evaporated, add another 1/2 cup of milk.
When the pork has become tender and all the milk has coagulated into small, brownish clusters, transfer the roast to a cutting board; tent with foil.
Tip the pot and spoon off most of the fat, being careful to leave behind all the coagulated milk clusters.
Add 2 or 3 tablespoons of water; boil away the water over high heat; use a wooden spoon to scrape loose cooking residues from the bottom and the sides of the pot.
Carve the roast into 3/8-inch slices and arrange on warm platter.
Spoon the pot juices over the pork; serve immediately.
