• Heat the oven to 350 F and butter the bottom and sides of a 9 to 10-inch tart pan, quiche pan, or cake pan.
• Combine the flour, baking soda, and salt in a medium bowl; stir or whisk to blend.
• In a large mixing bowl with an electric mixer, beat the butter and sugars for 3 minutes or until light and fluffy. Beat in the whole egg until well blended, then add the egg yolk and vanilla and beat until smooth. Add the dry ingredients and mix just until moistened; fold in the chocolate chips. You can save a few tablespoons for topping if you like.
• Spread the cookie dough in the prepared baking dish. If you saved some chocolate chips, sprinkle them evenly over the top and press them gently into the dough.
• Bake the chocolate chip cookie cake for about 22 to 24 minutes or until firm and golden brown. Transfer the pan to a rack and let the cake cool completely.
• If desired, remove the completely cooled cake from the pan and place it on a cake plate.
  

Prepare the Frosting

• Sift the confectioners' sugar and cocoa powder into a small bowl and stir to blend.
• In a mixing bowl with an electric mixer, beat 4 tablespoons of butter until it is smooth and creamy.
• With the mixer on the lowest speed, beat in the powdered sugar and cocoa mixture and 4 tablespoons of milk. Beat until smooth and fluffy, adding more milk, as needed for piping consistency.
• Fit a pastry bag with a decorative tip and fill it with the frosting. Pipe the frosting around the edge of the cake and finish with sprinkles. Enjoy!