Instructions

1. Preheat oven to 350 degrees F.  Spray a whoopie pie pan* with cooking spray and set aside.
2. In a large bowl combine flour, cocoa powder, espresso powder, baking powder, baking soda and salt.
3. In another large bowl beat butter, sugar, egg and milk and vanilla.
4. Make a well in the dry ingredients and pour in your wet ingredients.  Stir until just combined
5. Using a medium cookie scoop (1 1/2 tablespoons) place batter into wells of pan.  Bake in oven for 8-9 minutes or until a toothpick comes out clean.  Set aside to cool completely.

Marshmallow Buttercream

1. Into the bowl of your stand mixer fitted with the paddle attachment or in a large bowl, beat cream butter on medium speed until creamy.  Add marshmallow fluff.
2. Turn the mixer down to low and using 1 cup at a time, start to add your powdered sugar.  Mix well in between.  Add in milk and vanilla extract and beat until fluffy, about another minute.

Assembly

1. When the whoopie pies are cooled, pipe the marshmallow buttercream onto the bottom of your whoopie pies and place on the top whoopie pie to create a sandwich.

*If you do not have a whoopie pie pan, you can line a baking sheet with parchment paper or a Silpat and using a scoop, dollop 1 and 1/2 Tablespoons of batter onto prepared baking sheets, about 3 inches apart.

**I ended up using 2 1/2 cups of powdered sugar.