Make Ahead Baked Mashed Potatoes. Stir in milk and salt - up to two days ahead. Salt and freshly ground white pepper to taste.
8 ounces cream cheese. Mashed potatoes can be made almost completely ahead. Transfer the mashed potatoes to the prepared baking dish and spread into an even layer.
Sprinkle with the Parmesan.
1 cup sour cream. Bake until warmed through about 20 minutes. Stir in milk and salt - up to two days ahead. Transfer the mashed potatoes to the prepared baking dish and spread into an even layer.