Peel potatoes, if desired, and cut into 2-inch chunks. Place the potatoes and salt in a large heavy saucepan. Add cold water to cover by 2 inches. Bring to a boil. Reduce heat to simmer, cover, and cook until potatoes are very tender, 10 to 15 minutes. Drain well.
Transfer the potatoes to a large bowl. Mash with a potato masher, an electric hand-held mixer or by working through a ricer.
Stir buttermilk, chives, and pepper into the potatoes.