Place butter in a large bowl with electric mixer.
Beat the butter until creamy, about 1-2 minutes. If you're using a stand mixer (as opposed to a hand mixer) you will probably need to scrape the sides down once or twice.
Add the sugar and beat in until combined, about 1 minute.
Add the eggs, one at a time, followed by the egg yolks, scraping down the sides of the bowl as needed.
Add the baking powder, baking soda, and salt, and mix until combined.
Add the cake mix, mixing until combined.
Add the flour and cocoa powder, mixing until combined.
Add the chocolate chips and mix until combined.
Preheat the oven to 375 degrees F and line two baking sheets with parchment paper.
Form the dough into ½ cup sized dough balls. This recipe will make 8 large cookies.
Place 3 dough balls on each cookie sheet. Press additional chocolate chunks onto the tops of the cookies and slightly press the cookies down to flatten. If you want them super thick and less spread out, don't press them down to flatten.
Bake the cookies (one sheet at a time) for 9-10 minutes.
Cool on the cookie sheet for 10-15 minutes and then transfer to a cooling rack to cool completely. Since these cookies are so large, it's important to cool these completely, otherwise they may be too soft to pick up.
Repeat with the remaining two dough balls on the first baking sheet that you used.
Enjoy!