Mocha Whoopie Pies with Peanut Butter Filling

1. Position a rack in the center of the oven and preheat the oven to 375ºF. Line 2 baking sheets with parchment paper or nonstick silicone baking mats.
2. In a small bowl or cup, mix together the instant espresso powder and water and set aside. In a medium sized bowl whisk the flour, cocoa powder, baking soda, and salt.
3. In the bowl of a stand mixer fitted with a 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.
4. Add half of the flour mixture and half of the milk and beat on low until just incorporated. Scrape down the sides of the bowl. Add the espresso-water mixture and the remaining flour mixture and milk and beat until completely combined.
5. 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 1 sheet at a time for about 8-10 minutes each, or until the cakes spring back when touched. Remove the sheets from the oven and let the cakes cool on the sheet for about 5 minutes before transferring them to a rack to cool completely.

For the filling:
In the bowl of a stand mixer fitted with the paddle attachment, beat together the peanut butter and butter on low speed until smooth and creamy. Add the confectioners’ and beat until the filling is light and fluffy, about 4 minutes. Frost 1 whoopie pie with filling and top with another whoopie pie and viola!

Recipe from the cookbook Whoopie Pies by Sarah Billingsley and Amy Treadwell.