Potato Gratin

Ingredients

• 1 tablespoon unsalted butter, softened, for the dish
• 3 pounds Yukon Gold potatoes, peeled and sliced uniformly 1/8 inch thick; do not rinse or soak the slices
• 2 cups heavy cream
• 1 cup whole milk
• 2 garlic cloves, finely grated
• 1 1/4 teaspoons fine sea salt
• 1/2 teaspoon black pepper
• 1/8 teaspoon ground nutmeg
• 6 ounces Gruyère cheese, grated (about 1 1/2 cups), divided

Method

1. 1

   Step 1. Allow about 2 hours 15 minutes: 25 minutes preparation, up to 95 minutes baking and 15 minutes resting. Use a 9-by-13-inch baking dish of at least 3-quart capacity, a large bowl, foil, a rimmed sheet pan and an instant-read thermometer. Heat the oven to 375°F. Use a sharp knife, or a mandoline with its hand guard.

2. 2

   Step 2. Rub all the butter over the bottom and sides of the dish. Whisk the cream, milk, garlic, salt, pepper and nutmeg in a bowl until combined.

3. 3

   Step 3. Immediately toss the potato slices in the cream mixture, separating stuck slices so each is coated. Keep their surface starch; do not rinse them. Arrange half the slices in overlapping layers in the dish, scatter with 1/2 cup cheese, then add the remaining potatoes and all the cream mixture. Reserve the remaining 1 cup cheese for the top.

4. 4

   Step 4. Cover tightly with foil and set the dish on the sheet pan. Bake for 60–70 minutes. Carefully lift a corner of the foil and test the center with a thin knife; if there is firm resistance, cover and bake longer before topping. When almost tender, uncover, add the remaining cheese and bake for 20–25 minutes until browned and bubbling. The knife must pass easily through the center and the center must reach at least 165°F. If the top browns first, loosely cover and continue.

5. 5

   Step 5. Rest for 15 minutes so the cream thickens around the potatoes. Cut or spoon into eight side portions. Refrigerate leftovers promptly in shallow containers, within 2 hours (1 hour above 90°F), at 40°F or below. Use within 3–4 days; reheat to 165°F.