These mashed potatoes can be made-ahead two days before service. To reheat, place on stovetop with a splash or two of milk and a little butter. Heat on low, stirring occasionally. Be sure to purchase a boiling potato, my favorite is Yukon Gold. Do not use Russet. Lastly, make sure the butter is unsalted. If you choose to use salted butter use less salt to season the mashed potatoes.