How to Make It
Bring 12 cups water and potatoes to a boil in a large saucepan. Reduce heat; simmer 20 minutes. Add vinegar; simmer 10 to 15 minutes. Drain. Spread in a single layer on a baking sheet; cool.
Combine buttermilk and next 8 ingredients (through salt) in a large bowl. Stir in potatoes, breaking up slices slightly with a spoon. Stir in celery and pepper. Chill at least 1 hour.