Set the oven temperature to 350 degrees F.

Grease a 9-by-9-inch square baking pan with butter or shortening and line it with parchment paper. Put aside for now.

Whisk the flour, baking powder, baking soda, and salt in another bowl. Put aside for now.

Cream together the butter, light brown sugar, and granulated sugar in the bowl of a stand mixer.

Beat in the egg and vanilla to the butter/sugar combination until well incorporated.

Beat in the dry ingredients until they are well incorporated. Chocolate chips should be added and the mixture should be stirred until the chips are uniformly distributed. In a preheated baking dish, press the cookie dough evenly into the bottom. Sprinkle some more chocolate chips on top (if desired).

Allow to bake for 18-25 minutes, or until the top is lightly browned and the edges are firm.

The bars need to cool in the pan for at least 30 minutes after baking, so set the baking sheet on a cooling rack (preferably longer, they hold up better as they cool). Once the cookie bars have cooled, use the parchment paper to remove them from the pan.