Preheat your oven to 410 degrees.
In a big bowl, mix together the cold butter and sugars until it’s light and fluffy—this should take about 4 minutes. Add the eggs one at a time, making sure to mix well after each addition.
Now, add in the cocoa, cake flour, all-purpose flour, cornstarch, baking soda, and salt. Give it a good stir until everything is nicely combined. Then, toss in those peanut butter chips (or you can use chocolate chips if you prefer).
Let the dough chill for about 10 minutes.
Grab small portions of the dough and form them into large balls. Place them on a lightly colored cookie sheet. Gently press down on the top to smooth it out. These cookies are bigger than you think! You’ll be able to fit 4 cookies on one large sheet, and the dough will make 8 extra large cookies.
Bake them in the preheated oven for 8-11 minutes or until they turn a beautiful golden brown on top. After baking, give them at least 10 minutes to cool and set.