1 cup all-purpose flour
1/2 cup cocoa powder
1/2 teaspoon baking soda
1/4 teaspoon salt
2/3 cup firmly packed light brown sugar
6 tablespoons unsalted butter
3/4 teaspoon vanilla extract
1 egg
1 cup buttermilk

Filling:
2 1/4 cups confectioners’ sugar
5 tablespoons unsalted butter
3 tablespoons milk
1 teaspoon vanilla extract
1/8 teaspoon salt

Have all the ingredients at room temperature. Preheat the oven to 325 degrees. Grease and flour the wells of a whoopie pie pan. In a bowl, whisk together flour, cocoa powder, baking soda and salt; set aside. With a mixer, beat together brown sugar and butter on medium speed until combined. Add the vanilla and egg and beat until fluffy. Stop the mixer and scrape down the sides of the bowl. Reduce speed to low, and add the flour mixture in three additions, alternating with the 1 cup of buttermilk (beginning and ending with the flour). Beat each addition until well incorporated. Fill one well with batter. Tap the pan on the countertop to distribute batter evenly. This helps release any air bubbles. If the batter appears too thick, you may need to add an additional tablespoon of buttermilk. Bake until a toothpick inserted into the center of the cakes comes out clean, approximately 8-10 minutes. Transfer the pan to a wire rack and let cakes cool, then invert the pan to allow for easy removal of cakes. To prepare filling, beat together the confectioners’ sugar, butter, milk, vanilla and salt on low speed until combined. Increase speed and beat until fluffy. To assemble, spread the filling on the flat side of the cake and top with another cake, domed side up. Recipe makes approximately 12 whoopie pies.