Fill a large pot with water and place the beef inside.  Bring to a boil and then reduce heat to simmer for 3 hours or until tender.

Preheat oven to 350.  When tender remove the beef to a large baking pan.  Mix the preserves, sugar and mustard in a bowl.  Brush over the corned beef.  Bake in the oven until bubbling.  Let rest a few minutes and then slice thin.