Preheat oven to 375 degrees Fahrenheit and spray a 12" pizza pan with non stick spray.
In a large bowl, cream the butter, sugar, brown sugar, 1/2 of the vanilla and eggs.
In a separate bowl, whisk together the flour, baking powder and salt.
Stir the dry ingredients into the wet, and then add the chocolate chips.
Spread the dough onto the prepared pan and bake for 10 minutes.
To make the icing, whisk or sift together the cocoa powder and powdered sugar.
In a separate bowl, cream the butter and last half of the vanilla in a large bowl
Slowly add in the powdered sugar cocoa powder mixture, and milk as needed, until everything is incorporated and frosting is the right consistency.
Beat for 5 minutes to make sure it is fluffy.
Transfer the icing to a piping bag and decorate around the edge of the cookie.
Slice and serve.