Heat oven to 350 °F.
Line two baking sheets with parchment paper and set aside.
Cream together butter and sugars. On my mixer I used my paddle attachment and set my speed to low for 30 seconds, medium for 30 seconds, and then high for 30 seconds. It came out creamed and fluffy.
Add eggs one at a time.
Add vanilla, cake flour, all-purpose flour, baking soda, cocoa and mix for one minute or until fully incorporated.
Fold in broken Oreo cookies.
Scoop out cookie dough (heaping scoop ~2 T) and roll into balls. Pat them down so they are less than a 1/4 inch thin. They will puff up a bit when they bake.
Place flattened dough rounds on parchment paper. Do not overcrowd the sheet pan. I put ~6-8 cookies on a sheet pan.
Sprinkle crushed Oreos on top and pat into the dough. This will bind the cookies to the dough so they don't flake off when you eat them.
Cook for ~10 minutes.
Let cookies completely cool.