The hind leg, five to eight pounds, and the cut most Easter and holiday tables mean by lamb. Several distinct muscles of different thickness under one fat cap, which is why butterflying it — flattening the whole thing to an even depth — is usually the better decision than roasting it whole.
The leg runs from the hip through to the shank, containing the top round (inside), bottom round (outside), sirloin tip and eye — the same architecture as a beef round on a smaller scale. Sold three ways: whole bone-in with the shank attached, semi-boneless with the aitch bone removed, or boned and butterflied into a rough flat sheet. The muscles are separated by clean seams and differ substantially in thickness and tenderness, which is the central difficulty. Whole and bone-in, the thin end near the shank is well done by the time the thick sirloin end is medium-rare. Butterflied, everything is roughly the same depth.
A working limb, so more collagen than the loin and less than the shank, with modest intramuscular fat and a good external cap. The muscles are large enough to hold a temperature gradient, which cuts both ways — a whole leg gives you a range of doneness from the ends inward, which some people want, while a butterflied one gives uniformity. The leg has enough connective tissue that it can also be taken the other direction entirely: held for many hours above 170°F it converts and pulls, which is what a seven-hour gigot does. Both approaches work. The failure zone is the middle, around 150-160°F, where the fibers have contracted but the collagen hasn't converted.
Flattening removes the thickness problem entirely, cuts the cooking time to half an hour, and exposes far more surface to char.
HowBone it out or buy it butterflied, open to an even inch and a half — score the thick parts to flatten. Marinate with garlic, rosemary, lemon and oil. Hot direct heat, six to eight minutes a side, then indirect to 130°F. Rest fifteen.
The traditional presentation, and the bone conducts heat and adds flavour. Accept a gradient of doneness rather than fighting it.
HowStudded with garlic and rosemary, 450°F for twenty minutes then 325°F for the remainder — roughly fifteen minutes per pound to 130-135°F at the thickest point. Rest twenty-five minutes.
Goes the other way deliberately, holding the leg long enough above 170°F that the collagen converts and the whole thing pulls apart with a spoon.
How250°F, covered, with wine, stock and aromatics, seven hours. It is not carved; it's served in pieces. Completely different dish from the same cut.
A large roast benefits from arriving at temperature evenly and then browning, rather than browning first and cooking inward from a hot exterior.
How250°F to 120°F internal — around two hours for a five-pound leg — rest, then 500°F for ten to fifteen minutes to colour the fat cap.
A bone-in leg tapers from a thick sirloin end to a thin shank end, and the muscles inside differ in density as well. Cook to 130°F at the thickest point and the shank end has been past 150°F for half an hour; cook until the thin end is right and the centre is raw. This is not a technique failure, it is geometry, and no amount of resting or tenting changes it. The realistic options are to accept the gradient and serve people the doneness they prefer, which is how it has traditionally been done, or to butterfly the leg so the whole thing is one depth. What doesn't work is following a single temperature instruction on a whole leg and being surprised that half of it missed.
Butterflied is the more practical buy for most cooking and most butchers will do it if asked. Bone-in whole legs are five to eight pounds and feed eight to twelve; ask for the aitch bone removed, since it makes carving far easier and is difficult at home. Look for firm white fat rather than yellow, which indicates an older animal. American lamb is bigger and milder; New Zealand legs are smaller — often three to four pounds — and more strongly flavoured, which suits a marinade. If you buy boneless and rolled, unroll it and check the inside; some are tied around large pockets of fat and sinew that should have been trimmed.
Doneness: 130-135°F at the thickest point for medium-rare, resting twenty-five minutes for a whole leg — carryover on a piece this size can be eight to ten degrees, so pull early. Butterflied: 130°F. Seven-hour version: 190-200°F.
Bone-in has more flavour, cooks slightly more gently near the bone, and looks better on the table, but it carves awkwardly and cooks unevenly. Boneless and butterflied cooks evenly in a third of the time and takes marinade far better because there's more exposed surface. For a holiday centrepiece, bone-in. For anything you actually want to taste consistent, butterflied.
Twenty-five to thirty minutes for a whole leg, which is longer than people expect. A five-pound roast has enough thermal mass that carryover will raise the interior eight to ten degrees, so pulling at 130°F and resting lands you at 138-140°F. Cutting early also loses a substantial amount of juice, since the fibers haven't relaxed enough to reabsorb it.
For butterflied, yes — the exposed surface area makes it genuinely effective, and garlic, rosemary, lemon and oil for four to twenty-four hours changes the result. For a whole bone-in leg, marinade only reaches a few millimetres in, so studding it with garlic slivers and rosemary pushed into knife slits does far more than soaking it. Salt is the exception; salt penetrates and should go on a day ahead either way.