Preheat oven to 400° F and spray two baking sheets with cooking spray (or line with parchment paper).
Slice the cold butter into ¼ inch cubes and place in the standing mixer, along with the brown and cane sugars. Gradually increase speed and mix on high for 3-4 minutes until creamy. Scrape down the sides of the bowl halfway through.
In a separate bowl, whisk together the flour, cocoa powder, sea salt, cornstarch, and baking soda.
After creaming the butter and sugar, add vanilla extract and eggs. Mix on medium speed until well combined. Scrape down the sides of the bowl halfway through.
Add mixed dry ingredients to the standing mixer and mix on the lowest setting until just combined. Add chocolate chips while the flour is still mixing in--this minimizes the risk of overworking the cookie dough.
Roll the dough into 12 balls and place 6 on each baking sheet. If you'd like, press extra chocolate chips into the top of each cookie. Bake each sheet separately for 8-10 minutes. Mine are usually done right at 9 minutes. Allow the cookies to cool on the pan for at least 15 minutes before eating. Enjoy!