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Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.

Using a mandoline or a very sharp knife, thinly slice the peeled russet potatoes and sweet potatoes into 1/8-inch thick rounds. Try to keep the slices as uniform as possible for even cooking.

In a medium saucepan, combine the heavy cream, unsalted butter, fresh rosemary sprigs, pressed garlic, kosher salt, ground black pepper, and ground nutmeg. Heat over medium heat, stirring occasionally, until the butter is melted and the mixture is just simmering. Do not boil. Remove from heat and let steep for 5 minutes to infuse the flavors.

Arrange the sliced potatoes and sweet potatoes vertically in the prepared baking dish, alternating between russet and sweet potato slices to create distinct rows. Pack them snugly to ensure a stable structure.

Carefully remove the rosemary sprigs from the cream mixture. Pour the infused cream generously over the arranged potato and sweet potato slices, ensuring they are thoroughly coated and the cream seeps down between the layers.

Sprinkle the shredded Gruyère cheese evenly over the entire dish.

Bake for 50-60 minutes, or until the gratin is golden brown and bubbly, and the potatoes are tender when pierced with a fork. If the top browns too quickly, you can loosely cover it with aluminum foil.

Remove from the oven and let rest for 5-10 minutes before serving to allow the gratin to set.


Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.

Using a mandoline or a very sharp knife, thinly slice the peeled russet potatoes and sweet potatoes into 1/8-inch thick rounds. Try to keep the slices as uniform as possible for even cooking.

In a medium saucepan, combine the heavy cream, unsalted butter, fresh rosemary sprigs, pressed garlic, kosher salt, ground black pepper, and ground nutmeg. Heat over medium heat, stirring occasionally, until the butter is melted and the mixture is just simmering. Do not boil. Remove from heat and let steep for 5 minutes to infuse the flavors.

Arrange the sliced potatoes and sweet potatoes vertically in the prepared baking dish, alternating between russet and sweet potato slices to create distinct rows. Pack them snugly to ensure a stable structure.

Carefully remove the rosemary sprigs from the cream mixture. Pour the infused cream generously over the arranged potato and sweet potato slices, ensuring they are thoroughly coated and the cream seeps down between the layers.

Sprinkle the shredded Gruyère cheese evenly over the entire dish.

Bake for 50-60 minutes, or until the gratin is golden brown and bubbly, and the potatoes are tender when pierced with a fork. If the top browns too quickly, you can loosely cover it with aluminum foil.

Remove from the oven and let rest for 5-10 minutes before serving to allow the gratin to set.
