In a small saucepan over medium heat, add in the butter and melt. It will crackle and sizzle but continue to cook, stirring occasionally, about 10 minutes. The popping will quiet and the butter will begin to turn a light/auburn color and bit will form at the bottom. Remove from the heat once the color darkens more and transfer to a large bowl. Allow to cool for 5 minutes.
Add in the brown sugar and granulated sugar. Whisk to combine until there are no lumps.
Whisk in the egg and egg yolk one at a time and then the vanilla.
With a spatula or spoon, stir in the sifted flour, baking soda, cornstarch, sea salt, and espresso.
Fold in the chocolate chips until well incorporated. The batter will appear greasy but wet.
Cover with saran wrap and refrigerate for at least 3 hours.
Preheat the oven to 325℉ and line a baking sheet with parchment paper.
Using a cookie scoop or spoon, roll out 2 tablespoon heaping size cookie balls (about 1 oz. worth). Place them 1 inch apart from each other on the baking tray.
Bake for 10-12 minutes. They may appear slightly under cooked but allow them to rest for 5 minutes out of the oven on the pan to finish baking, Serve once cooled.