Preheat the oven to 350° F (180° C).
In a medium bowl, combine the dry ingredients except chocolate chips with a whisk or long-stem fork. Add the chocolate chips and mix until they are evenly distributed.
in a separate large bowl, using a mixer or whisk, whisk together the wet ingredients thoroughly until the mixture is completely homogenous. This may take 2-3 minutes.
Fold the dry mixture into the wet mixture until a smooth cookie dough forms.
Line a 9" cake pan with parchment paper by folding the paper into a wedge and cutting the wedge the size of the cake pan's radius (see images in "instructions" of this post).
Add the dough to the lined pan and use your clean hands to press the dough evenly into the pan.
Bake at 350° F for 10 minutes, then cover loosely with aluminum foil, and continue baking for another 20-25 minutes (see note 2), until the edges appear light brown and the center is slightly golden.
Once baked, remove the foil and allow the cake to cool at room temperature for about an hour before chilling in the refrigerator for 2-24 hours.
Gently remove the cake from the pan and transfer it to a serving plate. If using a cake pan, you can use a non-scratch utensil to cut around the cake and flip the cake onto a plate before flipping it again onto a serving plate.
Optionally pipe frosting using a star tip around the top perimeter of the cake and immediately add sprinkles. Slice into wedges and serve.
Store leftover cookie cake in an airtight container in the fridge for up to 2 days or the freezer for up to 3 months.