Put the oil and butter in a pot and turn the heat to medium. Add the onions, carrots, and celery. Stir to coat and cook until the onions have become translucent and the vegetables have started to soften, around 5 minutes.
Add the ground beef (or beef and pork if using both), a generous pinch of sea salt, and some cracked black pepper. Stir well and cook until the meat has lost its pink color. Add the milk and simmer gently, stirring frequently, until all liquid has bubbled away. After the milk has evaporated, add a tiny grating of the nutmeg and stir. Add wine and let simmer gently, stirring frequently, until all the liquid has bubbled away.
Next, add the crushed tomatoes and stir to coat. Reduce heat and cook, uncovered, for 2-3 hours, stirring from time to time. If the sauce starts drying out, add 1/2 C of water. At the end, however, no water should be left. Taste and season with sea salt and pepper. When ready to eat, toss cooked drained pasta with a tbsp of butter and top with a generous scoop of bolognese. If you like, finish with some fresh basil or parsley and grated Parmigiano Reggiano.