(1) Pass a large knife through the vent end of the bird just allowing the tip of the knife to show at the neck end.
(2) Cut through to one side of the backbone.
(3) Open the bird out flat and remove the backbone completely.
(4) Make an incision through the skin close to each leg and tuck the end of the drumstick through in order to hold the chicken in position.
(5) Turn the bird over onto a work-surface with the center bones exposed and lightly nick the breast bone once or twice — this will help to retain the shape of the bird during cooking.