For this slow-cooker take on mashed potatoes, the potatoes braise with just a little water, butter and salt, so the flavor of the potatoes and butter are pure and primary, buttressed by the tang of cream cheese and sharp cheddar. (You can also use this recipe as a basic guide and omit the cream cheese and cheddar before adding your own mix-ins or keep the potatoes unadorned.) Mashed potatoes are often thought of as something that must be made immediately before serving, but this method saves you the mad rush, as the mash can be held on the warm setting for up to three hours without any ill effect. You can also serve this directly from the crock. Don’t skip the rinsing step in the beginning; it helps keep the mash fluffy rather than heavy. And once you’ve folded in the cheese and cream cheese, resist further stirring and mashing, which can also affect the texture.