Heat the butter in a saucepan until it is all melted, darker in color, and the milk solids are caramelized. The butter should smell nice and nutty.
Chill the butter in the freezer for 10 minutes.
Mix together the flour, cornstarch, baking soda, and salt together in a small bowl and set aside.
Beat the butter and both sugars until light and fluffy.
Add in the egg, yolk, cream, and vanilla. Beat well.
Stir in the flour mixture and mix until just combined,
Fold in the chopped chocolate.
Portion the cookie dough into balls and set aside to rest while the oven preheats, preferably in the refrigerator.
Preheat the oven to 350°F. Line two baking sheets with parchment paper.
Place the cookie dough 2-inches apart on your baking sheets and bake for 8 - 10 minutes, or until golden brown.
Allow the cookies to rest on the baking sheet for one minute before transferring to a wire rack to cool completely. Top with flaky sea salt while still warm
Video
Notes
Allowing the cookie dough to rest is optional, but highly recommended. Check the post for tips on storage and baking success.