Preheat oven to 180 degrees C. Grease a 25x38cm Swiss roll tin.
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 tin.
Bake for 35 to 45 minutes in preheated oven. Cool in the tin on a wire rack. When completely cooled, cut into squares.