The most important aspect of this recipe, says Ross Lusted, is selecting the lamb. "It's the size of the shoulder that's important. You can get lamb shoulders that are three kilos, and they can be a bit scary - it's more mutton than lamb." You'll need to begin this recipe a day ahead.
Note Ask your butcher to bone and roll the lamb shoulder for you, leaving just the shank bone in. Ask to keep the remaining bones and trimmings for the lamb sauce. You'll also need to buy extra bones to make 600gm. The fat cap is the fat on the outside top of the lamb rack. Leave the other fat on. Greek oregano, also known as rigani, is more aromatic than the dried oregano sold in supermarkets. It's available in dried bunches from Greek delicatessens.