Boil up your lamb leg, feed it to the cat and go out to buy a whole shoulder of lamb on the bone. If your butcher removes the neck fillet yet still wants to sell it as "whole shoulder," change your butcher. Put the lamb into a big roasting tin, season it lightly and insert four or five sprigs of fresh rosemary into its cracks and crevices. Put it into an oven at 120°C and leave it untouched for at least six hours. You can whack the oven up for the last 20 minutes to crisp up the outside. Let it rest for at least half an hour. Believe me, you will never regret doing this. And you won't need a knife to "carve" it.

As for cooking it with garlic, I'd say that's fine (with whole cloves) if you have a big gathering who will help you to devour the whole lot. If you want meat for cold, however, it's best to leave the garlic out.