1. Preheat oven to 375°F (190°C) and butter a baking dish.
2. In a small saucepan, heat heavy cream with garlic, nutmeg (if using), salt, and pepper until warm but not boiling.
3. Arrange a layer of potatoes in the baking dish, slightly overlapping. Pour a little of the cream mixture over the potatoes and sprinkle with Gruyère cheese.
4. Repeat layers until all ingredients are used, finishing with a generous layer of cheese on top.
5. Cover with foil and bake for 40 minutes. Remove the foil and bake for an additional 20 minutes, or until the top is golden and bubbly.
6. Let rest for 10 minutes before serving for the best texture.