PREHEAT oven to 375° F.
MICROWAVE broken baking bars in small, uncovered, microwave-safe bowl on HIGH (100%) power for 1 minute; STIR. The pieces may retain some of their original shape. If necessary, microwave at additional 10 to 15-second intervals, stirring just until melted. Cool to room temperature.
COMBINE flour, baking soda and salt in small bowl. Beat butter, brown sugar, granulated sugar and vanilla extract in large mixer bowl until creamy. Beat in egg and melted chocolate. Beat in flour mixture. Stir in nuts. Drop by rounded tablespoon onto ungreased baking sheets.
BAKE for 8 to 9 minutes or until edges are set but centers are still slightly soft. Cool on baking sheets for 3 minutes; remove to wire racks to cool completely.