Preheat oven to 350 degrees F.
Line a 9x9” square baking pan with parchment paper and lightly grease. Set aside.
In a small bowl, mix together flour, baking soda, baking powder, and salt. Set aside.
In the bowl of a standing mixer, cream together butter, light brown sugar and granulated sugar until well combined.
Add egg and vanilla to the butter/sugar mixture and beat until combined.
Add dry ingredients and beat until all the ingredients are thoroughly combined.
Add chocolate chips and mix until evenly distributed.
Press the cookie dough into the bottom of the prepared baking pan.
Top with extra chocolate chips (if desired).
Bake for 18-25 minutes, or until the edges are set, and the top is just barely browned.
Place baking pan on a wire cooling rack and let the bars cool in the pan for at least 30 minutes (preferably longer, they hold up better as they cool).
Use the parchment paper to lift the cookie bars out of the pan, then cut into squares and serve.