Place 3/4 of the onions on the bottom of a baking dish.
Place ham on top of the onions, cut side down.
Using a rubber spatula, spread mustard over the ham. Pat sugar on top of the mustard. Sprinkle with cloves. Place remaining onions on top of ham. Pour water in the bottom of the pan.
Bake at 325° for approximately 20 minutes per pound of ham, occasionally basting the ham with pan juices. If the surface browns, tent foil over the top.
Slice and serve.