Preheat oven to 375 degrees. Rub a 2-quart baking dish with garlic, then lightly butter. Layer potatoes in dish, overlapping slightly.
In a medium saucepan, combine cream, 1 1/2 teaspoons salt, 1/4 teaspoon pepper, and pinch of nutmeg; bring to a simmer. Pour enough cream mixture into dish to just cover potatoes; cover dish with foil. Bake until potatoes are tender when pierced with a paring knife, 40 to 45 minutes. Remove foil and continue to bake until top of gratin is golden, 35 to 40 minutes. Let rest 15 minutes before serving.
To save time, use a mandoline or a food processor with slicing disk to cut the potatoes.