In a well greased 2-quart casserole place one-third of the potatoes; sprinkle with salt and pepper and dot with 1 tablespoon of the butter.
Top with half the onions; dot with 1 tablespoon more butter.
Repeat layers, ending with potatoes and the remaining butter.
Bake, covered, in a 325Â° oven for 1 hour.
Uncover; bake 30 minutes more.