Cover the potatoes with water in a large saucepan and add 2 tsp salt. Bring to a boil and cook until potatoes are tender, about 20 minutes (check with fork). Drain well.
Place the hot potatoes in a large mixer bowl. Using an electric mixer, beat until smooth. Add the butter and sour cream and whip for 20-30 seconds. Add the remaining 1 tsp salt, white pepper, and cheddar. Whip to incorporate. Add the cream and whip until the potatoes are smooth.