Preheat the oven to 350° F. Line a cookie sheet with parchment paper or a silicone liner and set aside.
In the bowl of a stand mixer, cream together the butter, brown sugar and granulated sugar until light in color and fluffy in texture.
Scrape the sides of the bowl and add in the egg, corn syrup and vanilla extract. Mix until combined.
Add the flour, cornstarch, baking soda and salt. Mix until a soft dough forms.
Mix in the dark chocolate chips until evenly distributed.
Portion out the dough using your desired size of cookie scoop. For small cookies, use a #40 (1 1/2 tbsp of dough) and for larger cookies use a #24 scoop (3 tbsp of dough).
Leave in a ball and arrange on the cookie sheet.
Bake at 350° F until the cookie spreads, flattens and begins to turn golden brown on the edges. For smaller cookies, 8-10 minutes, for larger cookies 10-12 minutes.
Immediately sprinkle with flakey sea salt, if desired.
Enjoy!