Classic Chocolate Whoopie Pie with Marshmallow Filling
For the Cake:
For the Filling:
To make the Cake:
Position a rack in the center of the oven and preheat the oven to 375°F (190°C; Gas Mark 5). Line two baking sheets with parchment paper.
Sift together the flour, cocoa powder, baking soda, and salt onto a sheet of waxed paper. In the work bowl of a stand mixer fitted with the paddle attachment, beat together the butter, shortening, and brown sugar on low speed until just combined. Increase the speed to medium and beat until fluffy and smooth, about 3 minutes. Add the egg and vanilla and beat for another 2 minutes.
Add half of the flour mixture and half of the milk to the batter and beat on low until just incorporated. Scrape down the sides of the bowl. Add the remaining flour mixture and 1/2 cup milk and beat until completely combined.
Using a spoon, drop about 1 tablespoon of batter onto one of the prepared baking sheets and repeat, spacing them at least 2 inches apart. Bake one sheet at a time for about 10 minutes each, or until the pies spring back when pressed gently. Remove from the oven and let the cakes cool on the sheet for about 5 minutes before transferring them to a rack to cool completely.
To make the Filling:
In the work bowl of a stand mixer fitted with the paddle attachment, beat together the Marshmallow Fluff and the vegetable shortening, starting on low and increasing to medium speed until the mixture is smooth and fluffy, about 3 minutes. Reduce mixer speed to low, add the confectioners' sugar and the vanilla, and beat until incor¬porated. Increase mixer speed to medium and beat until fluffy, about 3 minutes more.
To assemble the Whoopie Pies:
Spread filling onto the flat side of one cake using a knife or spoon. Top it with another cake, flat-side down. Repeat with the rest of the cakes and filling.
Alternatively, you can use a pastry bag with a round tip to pipe the filling onto the cakes, which will give you a smoother, neater presentation.