Active Time

　　50 minutes

　　Total Time

　　1 hour, 30 minutes

　　We combined the rich and indulgent cheesiness of Pommes Aligot and the beautifully swirled rosettes of Pommes Duchesse into one super-luxe casserole that looks fancy but is surprisingly simple to make.

　　

Ingredients

8 servings

　　4 pounds Yukon Gold potatoes, peeled, cut into 1 1/2" pieces

　　Kosher salt

　　4 garlic cloves, forced through a press or finely chopped

　　2 cups heavy cream

　　1/2 cup (1 stick) unsalted butter

　　3/4 teaspoon freshly grated nutmeg

　　3/4 teaspoon freshly ground white pepper

　　3/4 pound Gruyère, coarsely grated (about 4 cups)

　　1/2 pound fresh mozzarella, coarsely grated (about 1 1/2 cups)

　　

Special equipment:

A 4-quart gratin or casserole dish; a potato ricer or food mill; a pastry bag fitted with a 3/4-inch star tip

　　

Step 1

Place rack in middle of oven and preheat to 350°F. Place potatoes in a large wide heavy pot. Add 1 1/2 tsp. salt and enough cold water to cover by 2". Bring to a boil over high heat, then reduce heat to medium-low and simmer until potatoes break apart when pierced with the tip of a knife, 35–40 minutes.

　　

Step 2

Meanwhile, cook garlic, cream, and butter in a medium saucepan over medium heat, whisking occasionally, until butter is melted. Whisk in nutmeg, pepper, and 1 Tbsp. plus 1 tsp. salt. Remove from heat.

　　

Step 3

Drain potatoes and immediately pass through potato ricer into a large bowl. Stir in cream mixture until smooth.

　　

Step 4

Return half of potato mixture to wide pot; reserve remaining potato mixture in bowl. Add Gruyère and mozzarella and cook over low heat, stirring constantly with a wooden spoon, until cheese is melted and mixture can be stretched with the spoon (like warm mozzarella), about 10 minutes. Transfer to gratin dish; smooth top.

　　

Step 5

Working in batches if needed, spoon reserved potato mixture in bowl into pastry bag fitted with star tip. Pipe very tight rows of 1/2x1/2" rosettes on potato-cheese mixture in gratin dish. Bake until top is golden brown, about 45 minutes. Let stand 10 minutes before serving.