First make the master stock. Using a paring knife, remove any white pith from the orange peel as this will impart a bitter flavour to the stock. Roughly crush the rock sugar in a mortar with a pestle. Put the peel, sugar and all the remaining ingredients in a pan, bring to the boil, simmer for 30 minutes, then strain.
Place the lamb in the strained stock and slowly simmer for around 1½ to 2 hours. When the lamb is tender, remove from the heat and allow to cool in stock, then cut into individual ribs. Place in the fridge until completely cold (for best results, leave in the fridge overnight).
Toast the cumin, sea salt, coriander, fennel, chilli flakes and sesame seeds in a large frying pan until fragrant then set aside to cool in a large bowl. Very roughly crush using a mortar and pestle.
Add oil to a large saucepan or wok until it’s one-third to one-half full, for deep frying. Heat to 180°C. Prepare a tray lined with a rack for the cooked ribs. Deep-fry ribs in batches until golden brown. As soon as each batch of ribs come out of the oil, place on the rack to drain any excess oil. When the ribs are drained and have cooled, dust with a liberal coating of spices. Serve immediately.