In a mixing bowl, add cocoa, cake flour, all-purpose flour, cornstarch, baking soda, and salt and whisk together. Set aside.
In your stand mixer fitted with a paddle attachment, cream together cold butter and sugars until light and fluffy, about 4 minutes. Add eggs one at a time, mixing well after each addition.
Add in the cocoa dry mixture and stir until combined. Stir in semisweet chocolate chips.
Chill dough for 15 minutes. While the dough is chilling, pre-heat your oven to 410oF.
Separate dough into large balls and place on lightly colored cookie sheet. Lightly press on top of dough to smooth out. If you have a scale, you can make them anywhere from 4.5 ounces - 6 ounces. You will fit 4-6 cookies on one large cookie sheet. The dough makes 8-12 extra large cookies.
Bake for 9-11 minutes or until golden brown on the top. Let them rest for at least 10-15 minutes to set.