Note: If you did not get spiral sliced ham, use uncut one and just score skin on the top and sides of the ham with a knife. Make cuts across the skin that are about 1/4-1/2 inch deep, forming diamond shapes.
Combine ingredients for the glaze in a sauce pot and whisk until evenly combined. Bring the mixture to simmer over medium heat.
Let it simmer, stirring often, for about 10 minutes. Some of the liquid will cook off and the glaze will be thickened. Take off heat.
Preheat oven to 325°
Place a rack inside a roasting pan and add a couple of cups of water to the bottom of the pan.
Take ham out of the package and discard the packet of glaze that came with it. Place ham on a couple of sheets of aluminum foil and glaze it all over with about half the glaze. Reserve remaining glaze for later.
Wrap ham tightly in foil and place on the rack inside the roasting pan (flat side down if using half ham). Bake for about an hour covered.
Take ham out of the oven and open the foil. Raise oven temperature to 400°.
Glaze the ham all over and put it back in the oven, uncovered, for about 20-30 more minutes. The internal temperature close to the bone should be 140° when it's ready.
Take out the ham and let it rest for a few minutes before serving.