The ideal cut of lamb for this is the fillet that lies under the saddle, which you occasionally see in butchers' shops and supermarkets; otherwise the eye of the meat from the rump, saddle or best end is perfectly good, although will cost you a fair bit more. Season the lamb however you like, but remember one important thing: Never, ever salt it until just before cooking! Salt will leach the moisture out of the meat, leaving you with a bone-dry roast. The final step in preparing lamb fillet is to trim away some of the excess fat, leaving only a thin layer. Keep in the fridge in the original wrapping or in a covered container, below and away from cooked foods and any ready to eat food. Defrost thoroughly in the bottom of the fridge, below and away from cooked foods and any ready to eat food, before cooking. Never re-freeze raw meat that has been frozen and then thawed. Wash work surfaces, chopping boards, utensils and hands thoroughly after touching raw meat.