Remove skin from ham by cutting through the skin at the knuckle end of the ham, and loosening the skin at the broad end of the ham and pulling it gently away with fingertips. There will still be some fat left on the surface. Score the surface in diamonds or your own fancy pattern.
Rub ham well with brown sugar and stud with cloves in each diamond, or however it works with the pattern you've made. Cook in a large baking tray for 30 mins.
While it is cooking, melt the apricot jam and the Grand Marnier together over a low heat in a small pot. Remove ham from the oven after 30 mins and brush with this glaze.
Replace in tray and continue to cook for another 1½ hours.