You can make and chill these mashed potatoes (Yukon Golds make for a creamier, glossier mash) up to two days before the big night. Two days! Just reheat gently with a little more dairy and they'll be as velvety as if you had whipped them only moments ago. How does it work? When you combine the butter and the hot taters and then add the dairy, the butterfat coats the potato starches, preventing the dish from ever getting sticky, gluey, or gummy. True story.
- 4 lb. medium Yukon Gold potatoes, scrubbed
- 1¼ cups (2½ sticks) unsalted butter, cut into pieces
- Freshly ground black pepper
- A potato ricer or food mill fitted with fine disk
Place potatoes in a large pot and pour in cold water to cover by 1". Add a large handful of salt (water should taste briny, like the ocean) and bring to a boil. Reduce heat and simmer until potatoes are very tender but not crumbly, 30–40 minutes. Drain and return potatoes to warm pot to dry (off heat).
Meanwhile, heat ⅔ cup cream and ⅔ cup milk in a small saucepan over medium until just about to simmer. Reduce heat to low and keep warm until ready to add to potatoes.
Pass hot potatoes and butter through ricer into a large bowl (this will help combine them quickly; most of the skins should stay behind but pick out any small pieces that get through if you want); season generously with salt. Mix with a potato masher until butter is melted and combined.
Mixing constantly, gradually add warm cream mixture to potatoes, then mix in sour cream. Taste and season with salt and pepper as desired.
Do Ahead: Potatoes can be made 2 days ahead. Let cool; cover and chill. To serve, transfer potatoes to a small pot and add ⅓ cup heavy cream and ⅓ cup whole milk; reheat over medium-low, stirring often to prevent scorching.