Place the chicken on a board and run a sharp knife along one side of the breastbone, working your knife as close as possible down the carcass until you reach the leg. Pull the leg out of its joint so it lies flat and cut around the socket so the half chicken comes away from the carcass. Repeat with the other side. Remove the wing tip and bones from inside the leg by tracing the knife along the leg bones, skin-side down, and extracting them without causing too much damage to the skin.