Set aside 1/4 cup of the mini chips to sprinkle on the cookies. Melt one cup of the chocolate chips with 2 tablespoons of milk. Microwave on 50% power for one minute or until melted. Set this aside.
Cream together the butter and peanut butter until light and fluffy.
Add the sugar.
Add the eggs, 1/2 cup milk, vanilla and melted chocolate.
Add the flour, baking powder, baking soda, salt and cocoa powder. (You can add the rest of the chocolate chips at this point, but I forgot, I only added the ones to sprinkle at the end.)
Add the batter to the whoopie pie pan or drop onto cookie sheets 2 inches apart. Sprinkle with the remaining chocolate chips.
Bake in a preheated 350 degree oven for 9 minutes or until the tops are set. Let sit in the pan for one minute and transfer to a rack to cool. Now on to the best part. The frosting.
While the cookies are cooling you can get started on the best frosting I have ever had. Cream together the butter and peanut butter. When they are light and fluffy, add the marshmallow creme.
Add the powdered sugar and until combined. Add the milk until the frosting is the right consistency for spreading.
Put a generous blob of frosting on one cookie. Add another cookie and you have a whoopie pie.