Lamb shanks and leg roasts are both from the lamb's legs, as their names indicate, but they are handled very differently by cooks. The lamb's leg is a large and meaty cut, and it is relatively tender throughout. It is generally roasted, and a single leg can feed eight to 10 guests. The shank is the "ankle" portion of the lamb's leg, where the tendons and connective tissue gather together to anchor the muscles to the joint. Cooks allow one shank per diner, and slow-cook them until they are lushly fork-tender.
Heat the Dutch oven or heavy-bottomed roast pan over a moderately high burner. Add a small amount of vegetable oil. Sear the shanks one at a time, turning them so that every surface is well-browned, then set them aside on a plate or cutting board.
Dice the onion, carrot and celery and mound them into the bottom of your Dutch oven or roasting pan. Stir the vegetables until they are slightly browned, then remove the Dutch oven from the heat and arrange the vegetables into a pad for the shanks to sit on while they cook.
Place the shanks in the Dutch oven and season them lightly with salt and pepper. Add enough red wine and broth to cover the shanks, then the bay leaves, garlic and other seasonings if you are using any.
Cover the Dutch oven and keep it at a low simmer for one and a half to two hours, until the shanks are fork-tender. Alternately, place the Dutch oven in a preheated oven at 163 degrees Celsius for two hours, or until the shanks are fork-tender.
Cover the shanks loosely with aluminium foil and keep warm. Strain the cooking juices and spoon off the fat. Boil the juices rapidly in a small saucepan until they have reduced enough to coat the back of a spoon. Whisk in the cold butter, and serve the sauce alongside the hot shanks.
Use a sharp knife to trim away any loose pieces or excess fat from the leg. If the leg is boneless or semi-deboned, ensure that it is tied tightly and neatly.
Cut several small slits in the muscle and fat of the roast, and fill them with slivers of garlic. Rub the roast lightly with Dijon mustard, then season it lightly with salt and pepper. Transfer the leg to your roasting pan. Strip the needles from the stem of rosemary, and sprinkle them over the lamb.
Preheat your oven to 232 degrees Celsius. Put the lamb in the oven, and roast it at this temperature for 25 minutes to brown the surfaces.
Reduce the heat to 190 degrees C, and continue cooking until the thickest part of the leg tests at 51.6 to 54.4 degrees C when checked with an instant-read thermometer, after approximately 35 to 45 minutes. This will yield a medium-rare leg tending to rare in the thickest spots. Cook to a higher temperature if you prefer your lamb more done.
Remove the leg from the oven, cover it loosely with aluminium foil, and allow it to rest for 15 to 20 minutes before carving. Serve hot, with your favourite side dishes and sauce.
These two basic techniques are readily adaptable to any recipe. The flavours and specific ingredients will change, but the techniques are universal. Lamb shanks can be prepared in a slow cooker by the same method, but need to be seared separately in a skillet.