1. Remove silver skin from tenderloins, leaving a thin layer of fat. Combine brown sugar and next 5 ingredients in a large zip-top plastic freezer bag; add pork. Seal bag, and chill 8 to 18 hours, turning bag occasionally. Remove pork from marinade, reserving marinade.
2. Preheat grill to 350° to 400° (medium-high) heat. Grill pork, covered with grill lid, 8 minutes on each side or until a meat thermometer inserted into thickest portion registers 155°. Remove from grill, and let stand 10 minutes.
3. Meanwhile, combine reserved marinade and cornstarch in a saucepan. Bring to a boil over medium heat; cook, stirring constantly, 1 minute. Cut pork diagonally into thin slices, and arrange on a serving platter; drizzle with warm sauce.
*1 1/2 lb. flank steak may be substituted. Reduce grill time to 6 to 8 minutes on each side or to desired degree of doneness.