Preheat oven to 350 degrees F. Combine flour, cocoa, baking soda and salt in a medium bowl; set aside. Beat butter, sugar, brown sugar and vanilla extract in a large bowl until creamy. Beat in eggs. Gradually blend in flour mixture. Stir in chocolate chunks. Drop by rounded Tbsp 2 inches apart onto ungreased baking sheet. Bake 9-11 minutes or until cookies are puffed and centers are set but still soft. Cool on baking sheets for 2 minutes; transfer to wire racks to cool completely. Makes 3 dozen.