Place ham in a tall stock pot and cover with water. bring to a boil. reduce to low and simmer for 8 hours. remove ham from water. shred meat, removing any bones and fat.
Place shredded meat in a crock pot. in a separate bowl, combine mustard and brown sugar; pour over shredded ham and mix well, making sure that all the ham gets covered.
Cover and refrigerate overnight.
Reheat in the oven at 300 degrees for 2 hours prior to eating (if choosing this method do not place ham in a crock pot, rather, use an oven-safe dish), or place in a crock pot and cook on high for 2 hours.