Preheat the oven to 375° and lightly grease a 9 springform pan (preferred) or 9-inch cake pan.

In a medium bowl, cream the butter, brown sugar and granulated sugar together. Beat very well, about 60 seconds.

Add the egg, egg yolk, and vanilla to the bowl, and beat until combined.

In a small bowl, whisk together remaining ingredients (except chocolate chips) and add it in 2 batches to the creamed butter, beating just to combine.

Stir in the chocolate chips.

Press the dough into the pie plate and press it evenly flat. Scatter extra chocolate chips on top.

Bake for 23-27 minutes, until the middle is slightly underdone (it will set up as it cools).

Optional: make a half-batch of my chocolate buttercream, and decorate the cookie cake with it and sprinkles.