BRING sugar, sour cream and butter to full rolling boil in large heavy saucepan on medium heat, stirring constantly. Boil an additional 7 minutes or until candy thermometer registers 234°F, stirring constantly.
REMOVE from heat; stir in chocolate until melted. Add remaining ingredients; stir until well blended.
POUR into greased 8- or 9-inch square pan. Cool several hours or overnight. Cut into 64 squares to serve.