Boil the turnips, partially covered, in lots of salted water until they are cooked. You should be able to stab them with a fork, but they should not split. Drain the turnips, peel, and cut into bite-size pieces.
Melt the butter in a pot and then add the turnip pieces. Stir to break the pieces up, then add the sugar and vinegar and keep stirring until you have a thick mash. Stir in the c