Cut tops and bottoms off endives, remove cores near bottom, and wash. Bring water with a bit of vinegar to a boil. Boil endives eight minutes or until they're soft enough that you can poke a fork into the bottom. Put butter in pan and let endives drain. Wrap prosciutto around endive and brown on all sides. Wrap cheese around endive, put back in pan and cover, cooking on low heat until the cheese melts.