These Brown Butter Cookie Bars are basically super soft & chewy cookies but made in a pan!! You won't believe how easy & quick it is to make these bars!
To make the brown butter, start heating the room temperature butter in a saucepan over medium heat. Bring the butter to a boil and let it cook until brown in colour and nutty smelling, about 3-4 minutes total on the stove. Pour the brown butter into a heat-safe bowl to stop the cooking process. Let cool to room temperature before making the bars (about 20 minutes).
Preheat the oven to 350℉. Line a 9x9-inch pan with parchment paper, leaving the edges to hang over the sides.
Whisk together the cooled brown butter and brown sugar. Add the egg and vanilla and whisk until smooth. Stir in the flour and cream of tartar, incorporating just until no streaks of flour remain. Lastly, fold in the chocolate chips.
Transfer batter to the lined pan and spread into the corners and level with the spatula. Bake in the preheated oven for 20-22 minutes or until a toothpick inserted into the center comes out clean. Sprinkle with flakey salt and then let cool for at least 10 minutes before lifting out of the pan using the parchment paper as handles. Slice into 16 bars once cooled. Enjoy!