Active Time

　　25 min

　　Total Time

　　2 hr

　　Traditionally piped through a pastry bag into rosettes to garnish a roast, this classic French potato mixture is here transformed into a rich casserole that can be prepared in advance and is still the perfect match for a prime rib roast.

　　

Ingredients

Makes 8 servings

　　3 lb russet (baking) potatoes

　　1 cup heavy cream

　　5 tablespoons unsalted butter

　　1 garlic clove, minced

　　3 large eggs

　　1 1/4 teaspoons salt

　　1/4 teaspoon white pepper

　　3/4 teaspoon freshly grated nutmeg

　　

Special Equipment

a potato ricer or a food mill fitted with medium disk

　　

Step 1

Put oven rack in middle position and preheat oven to 400°F.

　　

Step 2

Prick each potato a few times, then bake in a shallow baking pan until tender, about 1 hour.

　　

Step 3

When potatoes are just cool enough to handle, halve and scoop out flesh. Force flesh through ricer or food mill into a bowl.

　　

Step 4

Heat cream with butter and garlic in a 3-quart heavy saucepan over moderately low heat until hot, then stir into potatoes. Beat in eggs 1 at a time with a fork until blended, then stir in salt, white pepper, and nutmeg. Spoon mixture into a buttered 2-quart (10-inch) round or oval shallow gratin or casserole dish. Bake until top is puffed and golden, 30 to 40 minutes.

　　Cooks' notes:

　　·Gratin can be prepared (but not baked) 1 day ahead and cooled completely, uncovered, then chilled, its surface covered with buttered wax paper and dish wrapped in plastic wrap. Bring to room temperature, about 1 hour, before baking.

　　·If you have only one oven, bake gratin while rib roast stands.