In a 3-quart saucepan, combine sugar, milk, and butter and boil until mixture reaches 236 degrees F on a candy thermometer (soft ball stage). Remove from heat and stir in remaining ingredients. Stir until chocolate is melted and mixture is well blended. Spread evenly into a buttered 9-inch square pan and cool until firm. Cut candy into pieces of desired sizes. Store in an airtight container in a cool, dry place.