Put the oil, butter and onion in the pot, turn the heat to medium and saute the onion until it becomes translucent. Add the celery and carrot. Cook for about 2 minutes, stirring the vegetables to coat them well.
Add the mince, a large pinch of salt and a few grindings of pepper. Break up the mince and cook until it has lost it's pink colour.
Add the milk and let it simmer gently, stirring frequently, until it has bubbled away completely. Add a tiny bit of nutmeg and stir.
Add the wine, let it simmer till evaporated, then add the tomatoes and stir thoroughly to coat all the ingredients well. When the tomatoes begin to bubble, turn the heat down so that the sauce cooks at the laziest of simmers, with just and intermittent bubble breaking through the surface. Cook, uncovered, for 3 hours of more, stirring from time to time. While the sauce is cooking you are likely to find that it begins to dry out. To keep it from sticking, add water as necessary. At the end, you want no water left.