In a large bowl or the bowl of an electric mixer, mix the butter until it is light and pale yellow. Add the sugars and mix until thoroughly combined and light. Add the eggs, one at a time, just until thoroughly combined. With the mixer running slowly, add the vanilla, then the dry ingredients, mixing just until combined. Finally, with the mixer running slowly, add the chocolate. You may need to finish mixing in the chocolate by hand so that it is thoroughly mixed throughout the dough.