Peel the potatoes and Jerusalem artichoke and cook in a little salted water. Then drain off the water. Then add the hot milk with butter, salt and nutmeg. Mix or mash as needed. Serve hot as a side dish.
Jerusalem artichoke gives the mashed potatoes a strong, somewhat earthy taste. So maybe use a little less Jerusalem artichoke on the first try (which, by the way, grows super and without any care in the garden and can be harvested all year round).