Peel and cube potatoes into 1-inch cubes.
Peel and thickly slice apples.
Cook potatoes and apples in boiling salted water until tender, about 10 to 15 minutes.
Drain.
Mash until smooth and creamy, adding butter.
Season with salt, nutmeg, and pepper.
Meanwhile, fry onion slices in about 2 tablespoons butter (or oil) until crispy.
Serve onions on top of mashed mixture either as a main or side dish for sausages or other meats.
