Preheat the oven to 350F. Add butter, brown sugar, and sugar to a bowl. Using a stand or hand mixer, mix for 4-5 minutes, until creamed and fully combined.
Add the eggs and mix until combined. Add flour, cocoa powder, cornstarch, baking soda, and salt. Mix until just combined.
Add chocolate chips and mix until the chips are evenly distributed throughout the dough.
Using a large scoop, about 1/4 cup, scoop the dough onto a lined baking sheet (you can definitely make smaller cookies, you'll just need to decrease the baking time). Press a few chocolate chips on the top of each dough ball (optional, butt gives a cool finished look).
Bake for 9-11 minutes. Allow to cool for at least 20 minutes. Enjoy!
p.s. these are very good with a scoop of vanilla ice cream!