Brown the butter. Place butter in medium-sized skillet and heat over medium/low heat until melted. Once melted, increase heat to just above medium and use a heatproof spatula to stir and swirl the butter constantly. Butter will begin to bubble, sputter, and pop. When the popping slows down you will see brown bits forming on the bottom of your pan. Once you see significant browning, remove from heat and pour into a heat-proof bowl.
Add bourbon, stir, and set aside to cool until butter is no longer warm to the touch. As the butter cools, preheat oven to 350F (175C), line baking sheets with parchment paper and set aside.
Once butter is cooled, add sugars and stir well.
Add egg, egg yolk, and vanilla extract and stir to combine.
In a medium-sized mixing bowl, whisk together flour, cornstarch, baking powder, baking soda, and salt.
Gradually add dry ingredients into the wet, stirring until completely combined.
Add chopped chocolate and stir well.
Scoop dough into 2 Tablespoon sized scoops (86g) and place on prepared baking sheet, spacing cookies at least 2” (5cm) apart.
Transfer to center rack of 350F preheated oven and bake for 10 minutes or until edges are beginning to turn light golden.
Upon removing from oven, sprinkle lightly with flaky sea salt. Allow to cool completely on pan before enjoying!
