01 - Preheat oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - In a large bowl, whisk together melted butter and brown sugar until smooth.
03 - Add the egg and vanilla extract and whisk until combined.
04 - Stir in the flour, baking powder, baking soda, and salt until just combined.
05 - Fold in the chocolate chips.
06 - Spread the dough evenly into the prepared baking pan.
07 - Bake for 22–25 minutes, or until the edges are set and a toothpick inserted into the center comes out with a few moist crumbs.
08 - Allow to cool completely in the pan before lifting out and slicing into bars.