Ask the butcher to French trim the lamb for you as it can be quite fiddly to do it yourself. It is difficult to judge whether a rack of lamb has been cooked to the preferred doneness. Take it out of the oven when you think that it is nearly ready and cut into it to check how much longer it needs. Cooking times can also vary, depending on the thickness of the fat on the lamb. Campari may seem like an odd thing to put in a sauce, but it offsets the sweetness of the orange well. If you really can't stand Campari, you can substitute Port, Brandy or Armangnac.