Score the top of the duck breast. Make the marinade: Mix all the above ingredients together except the chicken stock. Place the breast in the marinade and refrigerate for at least 2 hours. Remove the breasts from the marinade, pat dry and pan fry them in olive oil on both sides until they are brown. Place in the oven skin side down for 5 minutes, remove from the oven and leave to rest. Add the duck marinade to the chicken stock and reduce until the sauce reaches the right consistency, strain through a fine seive into a pan, season with finely milled pepper. Keep warm. Chefs tip: If you find it difficult to remove the zest from the grater use a pastry brush and brush down the grater on a slight angle, this seems to work well.