5 lbs white or yukon gold potatoes, peeled and cut into 2 inch chunks
2 1/2 tablespoons plus 1 tsp kosher salt
12 tablespoons unsalted buter, cut into pieces, at room temp
1/2 to 3/4 cup heavy cream
1 cup sour cream
1/4 tsp ground nutmeg
3/4 tsp black pepper
1. Place the potatoes and 2 1/2 tablespoons salt in a large pot. Cover with cold water. Bring to a boil. Reduce heat and simmer until tender, 20 to 25 minutes. Meanwhile, in a saucepan, over medium heat, heat the butter and 1/2 cup of the heavy cream until the butter melts.
2.Drain the potatoes and return to pot. Add the butter-cream mixture, sour cream, nutmeg, pepper, and the reamning salt. With a handheld potato masher, mash the potatoes. If a thinner consistency is desired, add the remaining cream, 1 tablespoon at a time.
3. Transfer the mashed potatoes to a heatproof serving dish. (You can cover the dish with aluminum foil and place it over a pot of simmering water, stirring occasionally, for up to 2 hrs).