Galette Lyonnaise

Peel the potatoes, boil in salted water until tender, and drain. Let them steam for a few minutes, then mash, until fairly smooth. Melt 3 T butter in a large pan and sauté onions until golden, then add half the remaining butter and the mashed potatoes. Season well with nutmeg, salt and pepper and stir thoroughly. Transfer to an enameled cast-iron gratin dish, smooth down, and dot the top with the remaining butter. Brown lightly in the oven or under the broiler. These potatoes are delicious with roast meats or steak.