Potato Gratin Recipe

Preheat and prep

Preheat oven to 375°F (190°C). Position a rack in the middle of the oven. Lightly grease a 9x9-inch (or 8x10-inch) baking dish with 1 tablespoon softened unsalted butter.

Wash and slice potatoes

Peel potatoes if desired (leave skins on for more texture). Using a mandoline or a very sharp knife, slice potatoes 1/8-inch (about 3 mm) thick. Rinse slices under cold water to remove excess starch, then pat dry with a clean towel or paper towels.

Grate cheeses

Grate the Gruyère and finely grate the Parmesan so they are ready to use.

In a medium saucepan or mixing bowl, combine 2 cups heavy cream and 1 cup whole milk. Stir in the minced garlic, fresh thyme leaves, 1 teaspoon salt, 1 teaspoon freshly ground black pepper, and a pinch of freshly grated nutmeg (if using). Warm the mixture over low heat until it's steaming but not boiling (about 3–5 minutes) to bloom flavors and help garlic soften. Remove from heat.

Arrange a single overlapping layer of potato slices in the bottom of the prepared baking dish to cover the surface. Sprinkle a thin layer (about 1/4 cup) of grated Gruyère and a tablespoon of Parmesan over the potatoes. Pour enough of the warm cream mixture over the layer to just come up to the top of the potatoes (do not fully submerge — aim for the cream to fill gaps and coat slices). Continue layering potatoes, cheese, and pouring cream mixture, pressing down gently on the stacks so the cream distributes evenly. Reserve about 1/4 cup Gruyère and 2 tablespoons Parmesan for the top.

After the final layer, pour any remaining cream mixture so the liquid reaches just below the top potato layer. Sprinkle the reserved Gruyère and Parmesan evenly across the top. Dot the top with 1 tablespoon softened butter. If using, sprinkle 2 tablespoons panko breadcrumbs for extra crunch.

Cover the baking dish tightly with foil and bake in the preheated oven for 40 minutes. Removing the foil for the final stage allows the top to brown.

After 40 minutes, remove the foil and continue baking for 20–30 minutes more, or until the potatoes are tender when pierced with a knife and the top is golden brown and bubbly. If the top browns too quickly, tent loosely with foil.

If you prefer a very brown top, place the dish under the broiler for 1–2 minutes, watching closely to prevent burning.

Remove the gratin from the oven and let it rest at least 10–15 minutes. Resting allows the cream to set so portions hold their shape when sliced.

Serve warm. Garnish with additional fresh thyme leaves if desired.