Step 1

Preheat oven to 350 degrees F and grease a (8 or 9 inch) pie plate or cake pan.

Step 2

Cream the butter and sugars together for 2 minutes and then mix in the egg, egg yolk, and vanilla.

Step 3

Add the dry ingredients and mix until combined. Use a wooden spoon to mix in all but 2 tablespoons of chocolate chips and then press the cookie dough into the pie plate. Sprinkle the remaining 2 tablespoons chocolate chips on top and press them down slightly.

Step 4

Bake for 22-25 minutes. Let the cookie cool completely and then run a sharp knife along the edge to loosen and then use a large spatula (or two!) to transfer to a platter. Pipe on frosting along the edges and add the sprinkles.

Step 5

Beat all the frosting ingredients together until smooth, adding milk as needed. Place into a piping bag fitted with a 1M tip. Pipe on frosting. Sprinkle on the sprinkles.