By removing the bone from the leg of lamb and flattening it out you can cook it more quickly. Marinades and flavourings also penetrate butterflied meat more easily due to its greater surface area. If preferred, ask your butcher to butterfly the meat for you.
-Rinse the leg of lamb thoroughly and pat dry. Cut off any membrane and excess fat.
-Feel for the triangular H-bone at the end of the leg. Cut around the bone using a sharp knife until it is almost free.
-Pull the H-bone to release it from the ball and socket joint, then cut it at the joint and discard.
-Working from the foot-end (opposite end) of the leg, cut along one side of the foot bone, freeing as much of the bone from the meat as possible.
-At the knee joint, (about two-thirds down the foot-bone), change direction, cutting along one side of the thigh bone in the same way to free the bone from the meat.
-Cut along the other side of the bones in exactly the same way, then remove the bones.
-Trim any remaining cartilage left on the meat.
-Make a deep incision in the thicker part of the leg meat, then open it out to form one flat, even piece of meat.
Source: https://www.bbc.co.uk
