Creamy Potato Gratin

1. Infuse the Cream Mixture

Start by combining the heavy cream, whole milk, smashed garlic, quartered shallots, freshly grated nutmeg, fresh thyme sprigs, whole black peppercorns, and Diamond Crystal kosher salt in a small saucepan. Bring this mixture to a gentle boil, then remove it from the heat. Cover the saucepan and let the mixture steep for an hour to infuse the flavors.

2. Strain the Cream Mixture

After the hour has passed, return the mixture to a boil. Once boiling, strain the mixture into a large heatproof bowl, pressing on the solids to extract as much liquid as possible. This step ensures that the cream mixture is richly flavored and smooth.

3. Slice the Potatoes

Meanwhile, peel the russet potatoes and slice them into 1/16-inch thick rounds using a mandoline. Directly add these potato slices into the hot milk mixture, stirring gently to coat them evenly. This not only ensures each slice is seasoned but also helps prevent the potatoes from browning.

4. Prepare the Cheese Mixture

Preheat your oven to 350°F (177°C). While the oven is heating, combine the grated Gruyère and Parmigiano-Reggiano cheeses in a small bowl. This blend of cheeses will add a wonderful depth of flavor to the gratin.

5. Layer the Potatoes

Grease a 2-quart baking dish with the softened unsalted butter. Begin layering the sliced potatoes in the dish, ensuring they are evenly distributed. After each layer, sprinkle a portion of the cheese mixture over the potatoes, repeating until all the potatoes are used. Leave the top layer of potatoes without cheese and pour any remaining milk mixture over the entire dish.

6. Bake the Gratin

Cover the baking dish with aluminum foil and bake for 1 hour. This allows the potatoes to cook through and the flavors to meld together. After an hour, remove the foil and sprinkle the remaining cheese mixture over the top. Bake uncovered for an additional 15-20 minutes, or until the top is lightly golden brown and the gratin is tender and thickened. This final uncovered baking crisps the top layer to perfection.

7. Let the Gratin Rest

Once the gratin is done, let it rest for 30 minutes before serving. This resting period helps the gratin set and makes it easier to serve. Enjoy the rich, creamy layers of this comforting dish.