Instructions

1. Cut 6 tablespoons unsalted butter into 12 pieces and let sit at room temperature to soften. Coat an 11x7-inch or other 2-quart baking dish with unsalted butter. Arrange a rack in the middle of the oven and heat the oven to 400ºF. Meanwhile, prepare the potatoes.
2. Peel 2 1/2 pounds Yukon gold potatoes and cut into 1-inch cubes. Place the potatoes and 2 tablespoons kosher salt in a large saucepan, and add enough cold water to cover the potatoes by about an inch. Bring to a boil over high heat. Reduce the heat and simmer until the potatoes are very tender and can be easily pierced with a sharp knife with no resistance, 10 to 12 minutes. Drain and set aside until the potatoes are cool enough to handle but still warm. Meanwhile, finely grate 2 ounces Parmesan cheese (about 1/2 cup).
3. Pass the warm potatoes through a ricer or food mill into a large bowl. Add the butter and 1/2 cup whole milk, and mix well until combined and the butter is melted.
4. Pour 1 cup cold heavy cream into the bowl of a stand mixer fitted with the whisk attachment. (Alternatively, use an electric hand mixer and large bowl). Beat on medium-high speed to stiff peaks, 3 to 5 minutes.
5. Stir 1/3 of the whipped cream into the potatoes. Gently fold the remaining whipped cream into the potatoes with a rubber spatula. Gently transfer the potatoes into the prepared baking dish. Sprinkle the Parmesan over the potatoes in an even layer.
6. Bake until the potatoes are warmed through and the cheese is lightly browned, 20 to 25 minutes. Let rest 10 minutes before serving.