Preheat oven to 410 degrees.
In large bowl, 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 cocoa, cake flour, all-purpose flour, cornstarch, baking soda, and salt and stir until combined.
Stir in semisweet chocolate chips.
Chill dough for 15 minutes.
Separate dough into large balls and place on lightly colored cookie sheet.
Lightly press on top of dough to smooth out. You will fit 4-6 cookies on one large cookie sheet. The dough makes 8-12 extra large cookies.
Press 5 or 6 chocolate chunks on top of the dough balls.
Bake for 9-11 minutes or until golden brown on the top.
Let them rest for at least 10-15 minutes to set.