Preheat oven to 350℉/175℃. Line a 9×13-inch pan with parchment paper, leaving enough overhang on the sides for lifting the bars out of the pan after baking.
In a medium bowl, sift together flour, baking powder, baking soda, and salt. Set aside.
In a large bowl, place the melted butter, granulated sugar, and brown sugar. Whisk until well combined. Whisk in the egg and vanilla extract.
Add flour mixture and fold, using a rubber spatula or wooden spoon, just until combined. Do not over mix. Fold in chocolate chips.
Spread dough evenly into prepared pan and smooth the top. Bake for about 25 minutes, until the top is golden brown, slightly firm to touch, and the edges start to pull away from the sides of the pan. The bars should appear soft but will set once cooled; over-baking will make them dry. Allow to cool to room temperature on a wire rack, then lift out of the pan and cut into squares.
- If you’d like to add nuts, reduce chocolate chips to 1 cup and add ¾ cup nuts. Walnuts, pecans, or hazelnuts are great.
- For a smaller batch: Cut the recipe in half, use an 8x8-inch pan, and bake for 20-25 minutes.
- Sprinkle bars with fleur de sel or coarse sea salt for sweet and salty bars.