Step by step

Method

5 steps

1. 1

   Heat the oven to 375°F. Rub a 9×13-inch baking dish with a halved garlic clove, then grease it with 1 tablespoon unsalted butter — the garlic leaves a light scent without raw bites.

2. 2

   Warm 1½ cups heavy cream with 1 teaspoon kosher salt, ¼ teaspoon black pepper, and ¼ teaspoon ground nutmeg in a small saucepan until steaming. Don't boil; you just want the cream hot so it soaks into the potatoes.

3. 3

   Peel and thinly slice 2 lb Yukon Gold potatoes (about ⅛ inch — a mandoline helps). Arrange half in overlapping layers in the dish. Pour over half the cream and sprinkle with ½ cup shredded Gruyère. Repeat with the remaining potatoes, cream, and ½ cup Gruyère.

4. 4

   Cover tightly with foil and bake 45 minutes. Uncover and bake 25–35 minutes more until a knife slides through the center easily and the top is deeply golden and bubbling at the edges.

5. 5

   Rest 10 minutes so the cream sets enough to slice. Scatter with fresh thyme leaves and serve warm. You want a creamy potato gratin with a browned cheese top — not watery undercooked potatoes or a scorched dry crust.