Scalloped Potato Gratin

Step 1

Heat oven to 350 degrees, and brush 1/4 cup butter on a rimmed 17-by-13-inch baking sheet. Brush one or two pieces of foil (enough to cover the top of the pan) with more butter. Set the foil aside.

Step 2

In a medium pot, bring the cream, sage, garlic, nutmeg, and a pinch of salt to a simmer. Simmer until reduced by a quarter, about 15 minutes.

Step 3

In a large heatproof bowl, lightly beat the eggs. Beating constantly, gradually add a little of the hot cream to the eggs, then slowly pour in the rest of the hot cream, whisking to prevent the eggs from curdling. Set aside.

Step 4

Using a mandoline or a sharp knife, slice the potatoes into 1/8-inch-thick rounds.

Step 5

Arrange one layer of potatoes on the buttered baking sheet, slightly overlapping the slices. Sprinkle with 3/4 teaspoon of the salt, add pepper to taste, then pour half the egg mixture over the potatoes. Top with 1/2 cup cheese. Repeat the layers of potato, seasoning and egg mixture. Top with the remaining 1 3/4 cups cheese. Cover the baking sheet with the foil (buttered-side down) and bake for 20 minutes. Remove the foil and bake until the potatoes and cheese are browned and bubbling, 25 to 30 minutes. Let cool slightly, then serve.