In a medium to large sized sauce pan, start browning the butter over medium heat. Cook it until you start to hear it make crackling noises. Once there is foam on top of your butter, and the color has turned auburn, you are done. Let it slightly cool for 10-15 minutes.
Preheat your oven to 325°F. Line a 8x8 or 9x9 pan with parchment paper, spray with non stick spray, and set aside.
In a medium sized bowl, sift together the cornstarch, baking powder, salt, and flour. Set aside.
In a small bowl combined the ¼ cup granulated sugar and 1 tablespoon of ground cinnamon. Set aside.
In a medium sized bowl, whisk the melted brown butter and the brown sugar until light and fluffy, about 3 minutes.
Whisk in the egg and egg yolk for 30 seconds and then add the vanilla. Whisk just until combined.
Switch to a rubber spatula and fold the dry ingredients into the wet ingredients. Just mix until there are no more signs of flour. Don’t over mix.
Pour the dough into the prepared pan. Evenly spread dough across the pan. Sprinkle the cinnamon sugar on top making sure to cover the whole top of the bars.
Bake for 22-25 minutes until the top is golden brown.
When the dough is done, let it cool completely before cutting. Serve at room temperature.