Potatoes Gratin (Gratin Dauphinois)

Serves 6-8.
1 clove garlic, halved
2 1/2 tbs butter or margarine
3 tbs lemon juice
6 cups water
5 (about 1 kg) medium thin-skinned potatoes
Salt,
pepper and ground nutmeg
3/4 cup thinly sliced green onions (shallots)
2 cups shredded Swiss cheese
1 1/2 cups light cream or milk
1 egg yolk
Rub a shallow baking dish liberally with garlic, then generously coat with about 1/2 tbs of the butter
In a large bowl, combine lemon juice and water. Peel potatoes if you want, cut into paper-thin slices, submerge in lemon-water until all are slices.
Drain potatoes well. Arrange about a quarter of the slices in an even layer in dish. Sprinkle lightly with salt and pepper and nutmeg; top with a quarter of the onions and 1/2 cup of the cheese. Repeat layers 3 more times, ending with the cheese.
Heat the cream or milk to scalding, pour slowly into egg yolk, beating constantly until blended. Pour egg mixture over potatoes. Dot with remaining 2 tbs butter.
Bake uncovered, in a 180 degree oven for about 1 1/2 hours or until potatoes are fork tender.