1. 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°.
2. Meanwhile, in a food processor, puree the chopped pineapple, then blend with the mustards.
3. Remove the ham from the oven. Turn the oven to 400°. Spread the pineapple mustard all over the ham and arrange the jalapeño rings on top in even rows. Bake the ham for 15 minutes, or until nicely browned. Transfer to a cutting board and let rest for 20 minutes.
4. Meanwhile, strain the pan juices into a saucepan and boil over high heat until reduced to 3 cups, about 20 minutes. Skim off the fat and pour the juices into a warmed gravy boat. Carve the ham in thin slices and serve with the pan juices.
Notes: Two mail-order ham sources: Dakin Farm (www.dakinfarm.com) and Karl Ehmer (www.karlehmer.com).