Soak the raisins in warm water. Combine the butter, salt, pepper and Cayenne pepper. Rub the lamb with the seasoned butter and put it on a spit. Leave to marinate for 30 minutes before placing in the oven. Roast until nicely browned, then insert a trussing needle in the thickest part of the meat near the bone. If the tip of the needle comes out a little hot, turn the oven off. The lamb will finish off cooking in its own heat. Prepare the sauce. Heat 1 tablespoon of olive oil in a saucepan, add the thinly sliced onions. Sweat them on a low heat until translucent. Brown the pine nuts in a frying pan with 1 drop of oil. Add the pine nuts and the raisins to the onions. Degrease the roasting pan, then deglaze with the vermouth, heated up with 1 tablespoon of boiling water. Scrape the drippings with the back of a fork. Pour the sauce on the pine nuts and raisins. Keep warm. Slice the roast and add the meat juice to the sauce, season generously and serve in a warmed sauceboat. Serve with pilaf rice.
