Preheat oven to 425 degrees.

Slice potatoes 1/8 inch thick and drop into a bowl of cold water.  Bring milk to a boil in a baking dish with garlic, salt, and pepper.  Drain potatoes, add to boiling milk, and distribute the butter over them.  Bake in the middle level of a preheated oven for about 25 minutes, until milk is absorbed, potatoes are tender, and the top has browned.  (If not served immediately, keep warm, uncovered, adding a bit more milk if potatoes seem dry.)