Prepare your lamb joint for roasting by rubbing it with a mixture of salt, pepper, and your choice of herb.
Place your shoulder onto the cast iron once your egg is up to temperature.
Grill the lamb shoulder on a hot barbecue for 3-4 minutes on each side until well colored butnot burnt. If flames flare up from dripping fat, gently move the lamb away fromthem.
Place the shoulder onto a baking paper lined with a double layer of foil. Loosely scrunch another double layer of foil over the top of the lamb.
Put the lamb shoulder on the barbecue grill. Close the lid, making sure the air vents are two-thirds closed on the top and bottom. Cook the lamb for 3 hours at 300 F.
Serve your lamb with all of your favorite side dishes.
