Set oven at Gas Mark 4, 180C (350F).
Heat the oil in a heavy casserole, large enough to take the lamb, and with a tight fitting lid. Brown the lamb. Add all the unpeeled garlic cloves, the herbs, lemon or lime and seasoning. Cover the casserole tightly with tin foil and then the lid and place in the pre-set oven for approx. 2 hours.
When the lamb is cooked, wrap in foil to rest before serving. Boil up the juices in the casserole.
Slice the lamb, pour some juices and some garlic cloves over each serving.
This recipe adapts well to a half leg or shoulder of lamb. Reduce the garlic if you wish.