Pre heat oven to 410 degrees.

In a large bowl or stand mixer, cream together cold butter and sugars until light and fluffy, about 4 minutes. Add eggs 1 at time, mixing well after each addition.

Add cocoa, cake flour, all purpose flour, cornstarch, baking soda and salt and stir until combined. Stir in chocolate chips.

Separate dough into large balls and place on a cookie sheet. Lightly press on top of the dough to smooth out.

Bake 9 to 10 minutes until until edges are crisp. Let them rest for 10 minutes.