Preheat oven to 425°.
Rub an 11- x 7-inch baking dish with cut sides of garlic halves; discard garlic. Coat dish with cooking spray.
Arrange half of potato slices in dish; drizzle with 1 tablespoon margarine. Sprinkle with 1/4 teaspoon salt and half of pepper; top with 1/4 cup cheese. Repeat layers with remaining ingredients.
Bring milk to a boil over low heat in a small saucepan; pour over potato mixture. Bake, uncovered, at 425° for 40 minutes or until potatoes are tender.