Gratin Recipe

Preheat and prep

Preheat oven to 190°C (375°F). Butter a 9x13-inch (or similar 8x8 if deeper) baking dish with 1 tablespoon of butter.

Peel the potatoes (optional) and slice them very thinly—about 2 mm (1/16–1/8 inch) thick—using a mandoline or a sharp knife. Rinse the slices and pat dry with a clean towel or paper towels. Sprinkle the potato slices with 1 teaspoon salt and set aside.

Peel and smash the garlic cloves. Rub the inside of the buttered baking dish with the smashed garlic, then discard the garlic (or leave it for a stronger garlic flavor).

In a medium saucepan, combine 1 cup heavy cream and 1 cup whole milk. Add the 2 smashed garlic cloves, 1 teaspoon freshly ground black pepper, and 1/4 teaspoon nutmeg.

Warm the mixture over medium-low heat until it just begins to steam and small bubbles form around the edges (do not boil). Remove from heat and let steep for 5 minutes to infuse the garlic flavor, then remove and discard the garlic cloves (or mince and leave them in for more garlic texture).

Arrange a single overlapping layer of potato slices across the bottom of the prepared dish so they lie flat. Sprinkle about 1/3 of the grated Gruyère and a tablespoon of grated Parmesan over the first layer.

Continue layering potatoes, seasoning lightly with additional salt only if needed between layers, and sprinkling cheese after every 2–3 layers. Aim to finish with a top layer of potatoes covered by the remaining cheeses. Reserve about 1/4 cup of Gruyère and the 1/2 cup Parmesan for the top.

Pour the warm cream mixture evenly over the layered potatoes so it seeps down between the slices. Press down gently on the potatoes to encourage the liquid to settle.

Dot the top with 2 tablespoons of unsalted butter cut into small pieces. Sprinkle the reserved Gruyère and Parmesan evenly over the top. If using, scatter 1 tablespoon fresh thyme leaves and 1/4 cup breadcrumbs for extra crispness; finish with 1/4 teaspoon black pepper.

Cover the dish tightly with foil and bake in the preheated oven for 40 minutes. Remove the foil and continue baking for another 20–25 minutes, until the top is golden brown and the potatoes are tender when pierced with a knife.

If the top browns too quickly, loosely tent with foil. For an extra golden crust, place under the broiler for 1–2 minutes—watch carefully to prevent burning.

Remove from oven and let rest for 10–15 minutes to set. This makes slicing cleaner and helps sauce thicken slightly.

Serve warm, garnished with additional thyme if desired.