In a medium bowl, sift together the flour and baking soda.
In a separate bowl, cream together the butter and the sugars until light and fluffy. Beat in the egg, egg yolk and vanilla. Slowly mix in the flour mixture until fully incorporated. Fold in the chocolate chips.
Scoop the batter onto a prepared baking sheet, and bake for around 15-17 minutes, or until the edges are browned.