Chocolate & Marshmallow Whoopie Pies

I've seen whoopie pies all over the internet and never knew what all the hype was. So I decided I should make some to find out. I choose these particular ones because I love chocolate and marshmallow. The cookie part is really just more like cake. Cake and frosting but in sandwich cookie form. They were very crumby and made quite a mess after I baked them. But they turned out great and we really liked them. The taste is also similar to a ding dong, but without the chocolate glaze on top. On more thing, the recipe says it yields 24 sandwich cookies. I made 1/2 the recipe thinking I would get 12 (since there's only 2 of us). I ended up with 27!! I made 1/2 the filling though and had JUST enough. I hate when recipes don't yield what they say!
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Chocolate Marshmallow Whoopie Pies
Annies Eats
Yield: about 24 sandwich cookies (not really though. Try 27 for 1/2 batch)
Ingredients:
For the cookies:
3½ cups all-purpose flour
1 tsp. salt
1½ cups unsweetened cocoa powder
1 tbsp. baking soda
1 tsp. baking powder
1 cup (2 sticks) unsalted butter, room temperature
2 cups sugar
2 large eggs
2 cups buttermilk, at room temperature
2 tsp. vanilla extract

For the filling:
1 cup (2 sticks) unsalted butter, at room temperature
2 cups confectioners’ sugar, sifted
7½ oz. marshmallow creme
2 tsp. vanilla extract

Directions:
Preheat the oven to 400˚ F. Combine the flour, salt, cocoa powder, baking soda, and baking powder in a medium bowl; whisk together to blend. Set aside. Line two baking sheets with silicone baking mats or parchment paper. In the bowl of an electric mixer fitted with the paddle attachment, combine the butter and sugar. Beat together on medium-high speed until light and fluffy, 2-3 minutes. Beat in the eggs one at a time, blending well after each addition. Blend in the buttermilk and vanilla extract until incorporated. Mix in the dry ingredients, blending just until combined.
Using a 1-oz dough scoop, drop the batter onto the prepared baking pans, 12 cookies per pan. Bake for 12 minutes, rotating the pans halfway through baking. Allow to cool on the pan 5-10 minutes, then transfer to a wire rack to cool completely. Repeat with the remaining batter.
To make the filling, place the butter in the bowl of a mixer fitted with the paddle attachment. Beat on medium-high speed until smooth, 1-2 minutes. Blend in the confectioners’ sugar until incorporated. Beat in the marshmallow fluff and vanilla until light and fluffy, 2-3 minutes.
Once the cookies are completely cooled, match them up in pairs by size. Fill a pastry bag fitted with a plain with the marshmallow filling. Pipe a dollop of marshmallow filling onto the flat side of one cookie of each pair, and sandwich the cookies together, pushing the filling to the edges. (Or just use a butterknife to 'frost' one of them then sandwich another on top. Much easier) Store in an airtight container.