Use a sharp knife to score the ham in a criss-cross pattern. Be sure to cut through the skin and fat to the flesh. You can completely remove the skin if you like, but I prefer to leave it on. Insert a clove at each intersection of your pattern.
Remove the leaves of the rosemary and rough chop them. Combine the marmalade and rosemary in a small saucepan over low heat.
Roast ham at 400 degrees F for 20 minutes. Pour half the rosemary and marmalade mixture over the ham, using a brush to spread it evenly in and around the pattern you cut, so the ham is well coated. Return to the oven for another 20 minutes.
Pour the remainder of the glaze over the ham and spread around. Return to the oven an additional 20 minutes.
Keep checking every 20 minutes,basting with pan drippings until ham is browned and glazed to your liking. An hour and 20 minutes, total, usually does it for me.