Rack of Lamb is cut from the upper part of the ribs, joined to the back bone. What is called “Lamb Ribs” is cut from the lower part of the rib cage, or the “spare ribs”, in the animal’s belly or “breast.”
Lamb Ribs are sold in slabs, though they can also be separated between the bone into “riblets.” Like pork spareribs, they have more bone and fat than they do meat, but lamb seems to have even more fat than pork does. The fat just needs low, slow cooking to allow it to render out, which is just as well, because what meat there is can be a bit tough, so it too requires low, slow cooking.
An average slab will be about 2 pounds (900g.)
Allow 2 per person as a main course (sic – remember, it’s a small slab, and most of the weight prior to cooking is bone and fat that will drip off.)
Some Australians like to put them in a baking dish or pan, on a rack, with some water underneath. That way the steam from the water moderates the cooking temperature, keeping it low and slow, and the rack allows all the fat to drip down underneath. You brush the ribs with a sauce before and a few times during cooking.
Compare that Australian method with the traditional Norwegian one of Pinnekjøtt.