Preheat the oven to 425 degrees F. Place the lamb in a roasting pan. Combine the remaining ingredients, except salt, in a small bowl. Brush mixture all over the lamb; season with salt. Roast 20 minutes, and then reduce heat to 325 degrees F. Cook lamb to desired degree of doneness, checking its progress with a meat thermometer. 80 minutes of additional cooking time should yield lamb that is medium rare, with an internal temperature of 135 degrees F.