Our Make-Ahead Mashed Potatoes Tips:
Keep Them Moist
To prevent the potatoes from drying out, top them with a thin layer of milk or half-and-half, then cover with a lid. Hold for up to 3 hours. Stir the milk in just before serving.
Makeshift Double Boiler
To keep mashed potatoes warm, or to reheat cold or leftover potatoes, transfer them to a large bowl set over a pot filled with a few inches of simmering water. (Make sure that the bowl does not come into contact with the water.)