Pommes Duchesse (Duchess Potatoes)

Adjust oven rack to middle position and preheat oven to 450°F (230°C). In a medium pot, combine potatoes, 2 quarts cold water, and 2 teaspoons salt. Bring to a boil over high heat, then reduce heat to maintain a simmer. Cook until potatoes are tender and offer little resistance when pierced with a paring knife, about 10 minutes. Drain potatoes, then return to now-empty pot. Serious Eats / Amanda Suarez Set pot over low heat and cook, shaking constantly, until moisture has evaporated from potatoes, 30 seconds to 1 minute. Remove from heat. Serious Eats / Amanda Suarez Using a ricer or food mill, pass potatoes into a medium bowl. Using a flexible spatula, stir in butter. Once butter is fully incorporated, stir in cream and nutmeg. Season with salt and pepper to taste. Stir in beaten egg mixture until combined, taking care not to over-mix the potatoes. Serious Eats / Amanda Suarez For Individual Portions: Line a rimmed baking sheet with parchment paper and grease lightly with nonstick cooking spray. Transfer potato mixture to a pastry bag fitted with a 1/2-inch star tip. To pipe the potatoes, hold the filled pastry bag at an 80° angle, apply steady downward pressure, and pipe a 3-inch-wide mound, working in a circular motion. To stop piping, cease applying pressure and swirl the pastry tip away. Continue to pipe portions about 2 inches apart, for a total of 12 portions. Lightly coat portions with clarified butter (if using), taking care not to undo the piped design. Serious Eats / Amanda Suarez For a Casserole: Grease a 2-quart baking dish, then set it on a rimmed baking sheet. Transfer 2/3 of potato mixture to prepared baking dish. Transfer remaining 1/3 to a pastry bag fitted with a 1/2-inch star tip. Using a flexible or offset spatula, smooth potato mixture in baking dish in an even layer. Pipe remaining potato on top by holding filled pastry bag at an 80° angle, and applying steady downward pressure to form small mounds in an even decorative pattern. Lightly coat portions with clarified butter (if using), taking care not to undo the piped design. Serious Eats / Amanda Suarez Transfer to oven and bake until golden brown, 15 to 20 minutes for individual portions, and about 25 minutes for a casserole; rotating baking sheet halfway through baking. Serve. Serious Eats / Amanda Suarez