Pour pan juices from baked ham through wire strainer, including onions and apples. Press on solids to extract as much juice as possible. Degrease strained juices. Add broth, sugar, and jelly to pan juices and heat to a boil in a saucepan. Mix cornstarch with mustard and sherry. Wisk rapidly into simmering sauce and stir for several minutes until blended and slightly thickened. Add currants or raisins and simmer 10-15 minutes before serving.