Set up your kettle for indirect normal fire cooking method, using approximately 25 barbecue briquettes in each charcoal basket. Light the fire-lighters and move the charcoal baskets to the center of the cooking grill over the flames.
With a sharp knife, cut the rind around the pork, around the knuckle and down the centre to free it on all sides, ensuring that you have cut right through the rind to the fat, but not into the flesh.
Approximately 35-40 minutes after lighting, all of the coals will be ashed over and ready for cooking. Separate the charcoal baskets using tongs. Place foil drip trays between the two fires- must be large enough to catch all of the drips. Place the cooking grill on the barbecue with the grill handles directly over the fires.
Place the pork on to the cooking grill. Close the lid, ensuring the air vents are open and positioned over the indirect zone. Cook for 2.5 hours to blister the skin.
To make the glaze, combine the butter and shallots in a saucepan over high heat until the shallots have cooked. Add the thyme, Riesling, red currant jelly, balsamic vinegar and black pepper. Continue to simmer for 10 to 15 minutes or until the glaze has thickened and caramelised, stirring often. Set aside to cool completely.
Remove the skin with tongs. Score the fat in a diamond pattern, being careful not to cut into the flesh, as the ham flesh will dry out.
Top up the charcoal baskets with additional barbecue briquettes. Add 3 wood chunks onto the coals. Continue to cook the ham for a further 30 minutes to render the fat before applying the glaze.
After 30 minutes of the ham cooking without the skin, decorate with the whole cloves. Apply a generous amount of the glaze over the ham and continue cooking for a further hour, glazing the ham every 20 minutes.
Once the ham has cooked, remove the ham from the barbecue and allow to rest for 15 minutes before carving.