These crowd-pleasing potatoes can be made up to a day ahead. Cool, cover, and refrigerate. Reheat to serve.
In large saucepan, simmer potatoes in salted water until soft, about 20 minutes. Drain well. Return to saucepan; add milk, cream, and butter.
Using a potato masher or an electric mixer, beat potatoes until fluffy. Beat in vinegar, mixing well. Add salt to taste.