Preheat oven to 375°F. Microwave 1 cup of the chocolate in microwavable bowl on HIGH 2 minutes or until chocolate is almost melted. Stir until chocolate is completely melted; set aside. Mix flour, baking soda and salt until well blended; set aside.
Beat butter and sugar in large bowl with electric mixer on medium speed until light and fluffy. Add egg and vanilla; beat until well blended. Stir in melted chocolate. Gradually add flour mixture, beating until well blended. Stir in remaining chopped chocolate. Drop heaping tablespoonfuls of dough, 2 inches apart, onto ungreased baking sheets.
Bake 11 to 13 minutes or just until golden brown. Cool on baking sheets 1 minute. Remove to wire racks; cool completely.