Preheat oven to 375.

Spray a 12" pizza pan with non stick spray.

Cream butter, sugar, brown sugar, vanilla and egg.

Whisk together flour, baking powder and salt.

Stir in dry ingredients, then chocolate chips.

Spread dough on prepared pan.

Bake for 10 minutes.

Whisk or sift together cocoa powder and powdered sugar.

Cream butter and 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 right consistency.

Beat for 5 minutes to make sure it is fluffy.

Transfer to piping bag and decorate around edge of cookie.