Preheat the oven to 450°. Cut off the ham skin, leaving a thick layer of fat. Lightly score the fat in a diamond pattern. Arrange the pineapple rings in a roasting pan. Add the onions, bay leaves, Marsala, Riesling, water and nutmeg. Set the ham on top, fat side up. Cover with parchment paper, then tightly cover the pan with foil. Bake the ham for 40 minutes. Turn the oven to 325° and bake for 2 hours and 30 minutes longer, or until an instant-read thermometer inserted in the thickest part without touching the bone registers 120°.