1. Cut the chicken whole open along the backbone and pull out the backbone.
2.Open up the halves and spread the chicken on the work surface
3. Break the breastbone by pressing on it hard with the hand.
4.Carefully lift the skin, season the meat with a little salt and push sage leaves under the skin.
5.Place the chicken in a shallow pan and brush the marinade on both sides.
6.Cover the chicken with vacuum-pack it and leave it to infuse in the refrigerator over night.
7.Barbecue the chicken bone-side down at medium heat and with the lid closed for 30 minutes.
8.You can weight it down with a heavy pan.
9.Then turn it over and finish-barbecue it in about 10 minutes. The chicken can be served when the leg is pierced, the escaping juice has no blood in it.