In a 2-qt. microwave-safe bowl, combine sugar, milk and butter. Microwave on high until mixture comes to a full rolling boil, stirring after 2-1/2 minutes. Cook 3 minutes more, stirring after 1 minute. Add marshmallows; stir until melted. Stir in chips and chocolate until smooth. Stir in nuts and extracts. Immediately pour into a greased 11x7-in. pan. Chill until firm. Cut into squares. Store in the refrigerator.