Spread ice cream over chocolate layer filling. Cover with foil; freeze 4 hours or until firm. Just before serving, in a heavy saucepan, combine all sauce ingredients except vanilla; mix well. Bring to a boil over medium heat, stirring constantly. Reduce heat to low; cook 5 minutes, stirring constantly. Remove from heat; stir in vanilla. Let stand at room temperature 10 minutes before serving. Cut dessert into squares; drizzle warm fudge sauce over each square.