PREHEAT oven to 350º F.
COMBINE flour, cocoa, baking soda and salt in medium bowl. Beat butter, granulated sugar, brown sugar and vanilla extract in large mixer bowl until creamy. Add eggs, one at a time, beating well after each addition. Gradually beat in flour mixture. Stir in chunks. Drop by rounded tablespoon onto ungreased baking sheets.
BAKE for 9 to 11 minutes or until cookies are puffed and centers are set but still soft. Cool on baking sheets for 2 minutes; remove to wire racks to cool completely.