Preheat oven to 400 degrees F. In preparing the lamb: Trim any fat from the meat. Remove the pelvic bone which is made up of the hip bone and aitch bone. It runs at an angle to the leg bone and is attached by a ball and socket joint. To loosen it, place the leg on a board, pelvic bone upward. With a sharp knife outline the edges of the bone that are exposed at the sirloin end. Cut deeper around the pelvic bone, freeing it at the joint and cutting through the tendons connection it to the leg bone.
Remove the bone. Grasp the shank bone at the tip of the leg and cut all tendons at the base of the bone.
Cut the meat away from the bone, keeping the meat on the outer side in one piece. When the bone is clean, locate the knee joint at the point where the shank bone is connected to the leg bone. Cut the tendons are the joint and remove the shank bone. The last bone to remove is the leg bone. Remove by "tunnel fashion." Cut and scrap to clean the cone, easing it out as you work. Twist the bone and pull it out. Scrape the tendons one by one from the meat. Butterfly the meat.
For the Chili Rub: Combine all the ingredients together in a bowl to form a rub. The mixture should be moist but not wet.
Yield: 15 servings