Cut potatoes into enough thin slices to measure about 4 cups. Rub oblong baking dish, 10" x 6" x 1 1/2", with cut garlic clove; brush with 1 tsp. margarine. Arrange potatoes in 3 layers in casserole, sprinkling each layer with 1/3 each of the salt, nutmeg, pepper and cheese.
Beat eggs and half-and-half; pour over potato slices. Dot with 1 Tbsp margarine. Cook uncovered in 350-degree oven until potatoes are tender and top is golden brown, about 1 hour.