Personally, I'll take a whoopie pie over a cupcake any day and this recipe is the best I have found. In fact, it is so perfect that I will stop trying out other recipes and use it exclusively. When Tinker Bell took a bite she said, "there are no words for how good this is." I agree!! Then she said, "you're pretty good at this baking stuff." Aw, shucks.
But the best part of this recipe is that the little pies are even better the next day. They should be wrapped in plastic wrap and stored in the fridge, but allow them to come to room temperature before eating.
For the cakes:
2 cups flour
1/2 cup Dutch-process cocoa powder (it has a stronger, deeper flavor than regular cocoa)
1 1/4 tsp baking soda
1 tsp salt (I used less, about 1/2 tsp)
1 cup buttermilk
1 tsp vanilla
1 stick butter, softened (I used Smart Balance 50/50)
1 cup brown sugar
1 egg
For the filling:
1 stick butter (again, I used Smart Balance)
1 1/4 cups powdered sugar
1 cup Marshmallow Fluff
1 tsp vanilla
Combine the flour, cocoa, baking soda, and salt in a bowl and set aside. Combine buttermilk and vanilla in another, small bowl and set that aside. Beat the butter and sugar together in mixer on medium speed until fluffy, about 3 minutes. Add the egg and beat until combined.
With mixer on low, alternate adding the flour mix and buttermilk mix, beating after each addition. Begin and end with the flour mixture. Grease or line with parchment at least two cookie sheets. I used two large and one small and greased them with cooking spray--I was out of parchment paper. The original recipe calls for using a 1/4 measuring cup, but I just used a large soup spoon and got 24 cookies total, which makes a dozen whoopie pies. Using a 1/4 cup with give you 9 pies total.
They are not exactly round and perfect, are they? It won't matter when you eat them!
Bake at 325 for 13 minutes, let set on the cookie sheets for 2 minutes, then transfer to a rack to cool.
While they are cooling (and they do need to be completely cool before frosting), beat together the butter, sugar, marshmallow, and vanilla on medium speed until smooth. About 3 minutes or so.
I turned over 12 of the 24 cookies and evenly distributed the unbelievably delicious filling amongst them, then topped them with the remaining cookies.
We couldn't wait until the next day and ate, well, most of the pies right after they were made. I stacked the leftovers on a plate, covered them in plastic wrap and put them in the fridge. The next day...oh, wow. Perfection.