Trim the fat from the meat. Stir together the mustard, honey, curry powder, and 1 teaspoon of chives. Measure about 1 tablespoon of the mustard mixture, and brush over the meat. Insert a meat thermometer into the center of the meat. For the sauce, in a small bowl combine the remaining mustard mixture and sour cream. Cover and chill until serving time. In a covered grill arrange the medium coals around a drip pan. test for medium low heat above the pan. Place the meat on a grill rack over a drip pan. Cover and grill to desire doneness. Allow 1 1/4 to 1 3/4 hours for medium rare 1 3/4 to 2 1/4 hours for medium. Remove the meat from the grill and cover with foil. Let it stand for 15 minutes before slicing. *The meat's temperature will rise 5ºF.  during standing. Serve the meat with sauce and if desired, additional snipped chives. Makes 12 servings.