Preheat oven to 300 degrees F. Line a 9 by 13-inch baking pan with parchment paper. (Parchment paper is sold in the same aisle as wax paper). In large bowl, beat butter, vanilla and sugar until lightened. Beat in eggs one at a time. Sift together flour, baking soda and baking powder, and slowly blend this mixture into the wet ingredients. Mix in chocolate chips. Press cookie dough evenly into the pan.
Bake 55-60 minutes. Remove from oven and cool completely. Cut around the outer edges of the pan. Place a cutting board on top of the pan. Invert to unmould the 'large cookie.' Cut into quarters, and then cut each quarter into 15 squares. Cookie squares freeze well.
Makes 60 squares.