In a bowl, mix the salt with the sugar, cumin, coriander, pepper and cinnamon.
Transfer 2 tablespoons of the rub to a medium bowl.
In a large, shallow baking dish, sprinkle the remaining rub over the lamb ribs, massaging it into the meat. Let stand at room temperature for 1 hour.
Light a gas grill. Whisk the apple cider vinegar and pomegranate molasses into the reserved 2 tablespoons of rub.
Transfer the lamb ribs meaty side down to the braai and cook over moderately low heat, turning once, until lightly charred all over, 7 to 10 minutes.
Reduce the heat to low and grill, turning and basting with the sauce every 10 minutes, until the meat is very tender and nicely charred, 1 hour and 30 minutes.
Transfer the ribs to a carving board, tent with foil and let rest for 10 minutes. Cut the ribs between the bones and serve.
