To cook it quickly, trim off any large pieces of fat but leave the skin intact.
Put the lamb on a board, flesh side up and slice halfway through the thickest parts of the meat (but not right through) so that the thickness of the entire cut is more uniform.
Place in an ovenproof roasting dish, skin side up.
Make small incisions with a small sharp knife all over the skin and push a small slice of garlic and a small sprig of rosemary into each incision.
Drizzle with olive oil and sprinkle with salt and freshly ground black pepper.
Place in a preheated 200°C oven for 20 minutes or until you see beads of rose coloured juices on the surface of the lamb.
Remove from the oven, transfer to a platter, cover loosely with foil and rest 10 minutes.
Remove the foil then cut the whole cut in two pieces. Slice each half across the grain of the meat to serve.
You can also cook this cut on a moderate heat barbecue.
To long-cook, follow the instructions for the Lamb Oyster Shoulder.