The key to a successful sauce is to use a sharp knife rather than a food processor. A mezzaluna is the perfect implement. See how to use a mezzaluna here a chopping knife will do just as well!
To spatchcock (split open and grill) a chicken, place it on a board breast side down, with the legs towards you. Using poultry shears or a strong pair of scissors, cut right along the backbone and through the ribs on either side of the parson’s nose. Lift out the backbone, open out the chicken and turn it over. Now press down with the heel of your hand so that the meat is all one thickness. Insert two skewers diagonally through the breast and thigh meat to secure the legs and keep the bird flat.