Preheat oven to 350 degrees F (175 degrees C). Grease a 10x15 inch jellyroll pan.
In a small bowl, combine flour, baking powder, and salt. Set aside. In a large bowl, cream together the butter, white sugar, brown sugar, and vanilla until smooth. Beat in the eggs, one at a time, then stir in the flour mixture. Mix in chocolate chips, if desired. Spread the batter evenly into the prepared pan.
Bake for 35 to 45 minutes in preheated oven. Cool in the pan on a wire rack. When completely cooled, cut into squares.