The afternoon before you plan to serve the ham, fill a very large kettle or pot, or your sink, with water. Soak ham 4 to 8 hours to lose some of the saltiness; change the water two or three times if possible. Rinse well, and scrape off any mold or green rind.
Wrap ham well in aluminum foil. Place on a baking sheet. At 7 p.m. the night before you plan to serve the ham, preheat the oven to 500 degrees. Place the wrapped ham in a large roasting pan filled with 1 inch of water, and bake for 30 minutes. Turn off the oven, but do not open the door. At 10 P.M. turn the oven back on to 500 degrees. Bake the ham for 15 minutes more. Turn off the oven, but do not open the door. Leave the ham in the closed oven overnight.
Remove ham from the oven, then remove the aluminum foil. Using a very sharp knife, trim the rind and all the fat from the ham. Serve the ham warm or at room temperature; cut with a ham-slicing knife into very thin slivers.