Preheat the oven to 400°F. In a large bowl, whisk together the all-purpose flour, cake flour, cacao powder, cornstarch, baking soda, baking powder and salt. Set aside.
Place the cold, cubed butter into the bowl of a stand mixer and secure the paddle attachment. Turn the mixer on the lowest setting.
Let the mixer cream the butter for about ~30 seconds, and then add in the brown sugar and mix for ~30 seconds, followed by the white sugar until fully incorporated.
Then add in the egg, egg yolk and vanilla extract. Blend until mixed. If any of the mixture gets stuck on the paddle attachment use a rubber spatula to knock it off.
Keep the mixer on low speed and gradually add in the dry ingredients. I add in about ¼ cup at a time. Lastly, add in the chocolate chips until incorporated and then turn off the machine.
Measure out 6 large cookies. Roll each cookie dough ball generously in the confectioners’ sugar. Place the cookies on an ungreased cookie sheet and gently press cookies down just a little to flatten them.
Double up the cookie sheet. Meaning, flip one cookie sheet upside down and place the cookie sheet the cookie dough balls are on on top of that. This ensure the bottoms won’t brown too much. It’s a fun trick!
Bake the cookies for 10-12 minutes (I always bake for 10 in our oven). The secret is to pull them out before you think they are done. Let them rest on the cookie sheet for 15 minutes and then using a spatula transfer them to a cooling rack. Enjoy!