Make-ahead Mashed Potato Casserole
5 pounds baking potatoes (such as russets), peeled and cut into 2-inch chunks
8 ounces cream cheese, cut into chunks, at room temperature
1 cup sour cream
½ cup whole milk
½ cup (1 stick) unsalted butter (6 tablespoons at room temperature, 2 tablespoons cut into small cubes), plus extra
Kosher salt and ground black or white pepper
Place the potatoes in a large pot, then add enough cold water to cover them by 1 inch. Add a generous spoonful of salt, then cover the pot and bring to a boil over high heat. Set the lid ajar and reduce the heat to medium-low. Cook the potatoes at a steady simmer until they are barely tender when pierced with the tip of a small, sharp knife, 20-25 minutes. Drain the potatoes well.
Return the potatoes to the pot. Cook them over medium-low heat, stirring almost constantly, until the potatoes begin to film the bottom of the pot, about 3 minutes. Add the cream cheese. Using a handheld electric mixer, whip the potatoes until the cream cheese melts. Add the sour cream, milk and the 6 tablespoons room temperature butter. Mix well. Season to taste with salt and pepper.
Use a bit of butter to lightly coat a 13-by-9-inch baking dish. Transfer the potatoes to the baking dish, smoothing the top. Dot the top of the casserole with the 2 tablespoons of cubed butter. Let cool completely. Cover with plastic wrap and refrigerate for up to 1 day. Remove from the refrigerator 1 hour before the final baking.
When ready to reheat, position a rack in the center of the oven and heat the oven to 375 degrees.
Uncover the casserole. Bake it until the top is lightly browned and the casserole is heated through, about 30 minutes. Serve hot.
Adapted from "The Big Book of Sides" by Rick Rodger (Ballantine Books, 2014)