Chocolate-Peanut Butter Whoopie Pies

To make the most decadent whoopie pies, use the darkest, richest cocoa powder you can get your hands on for the cakes. I used Hershey's Special Dark. For the creamiest, most addictive filling, I use Skippy.

Makes 8 4-inch pies

For the cakes:
2 cups all-purpose flour
1/2 cup dark unsweetened cocoa powder
1 1/4 teaspoons baking soda
3/4 teaspoon salt
1/2 cup (1 stick) unsalted butter, at room temperature
1 cup light brown sugar
1 teaspoon pure vanilla extract
1/2 teaspoon instant espresso powder
1 large egg
1 cup well-shaken buttermilk
1/2 cup mini semi-sweet chocolate chips

For the peanut butter filling:
1 cup smooth peanut butter
1/2 cup (1 stick) unsalted butter, at room temperature
1 cup confectioners’ sugar, sifted
1/4 teaspoon salt

Position the oven racks to the upper and lower thirds of the oven and preheat it to 350 degrees. Line two baking sheets with parchment paper or silicone baking mats.

In a large bowl, sift together the flour, cocoa powder, baking soda and salt.

In the bowl of an electric mixer, beat together the butter, brown sugar, vanilla and espresso powder until light and fluffy, about 2 minutes. Beat in the egg. Reduce the mixer speed to low and stir in the buttermilk. The mixture will look funky—curdled, terrible. But press on, it will smooth out when the dry ingredients are added.

Keeping the mixer on low, gradually add the dry ingredients. Increase the speed to medium and beat just until the batter is completely smooth, about 30 seconds. Fold in the mini chocolate chips by hand.

Scoop the batter onto the prepared baking sheets into level 1/4 cup portions, 8 scoops to a sheet (a standard ice cream scoop is perfect for this task). Bake until the tops of the cakes spring back when lightly touched, 12-15 minutes. Let cool on the pan for five minutes before removing to a wire rack to cool completely.

To make the filling, beat together the peanut butter, butter, confectioners’ sugar and salt on medium-low speed until smooth. Crank the speed up to high and beat until lightened in color and texture, about 1 minute. Dollop the filling onto half the cakes (1/4 cup of filling per whoopie), and sandwich with the remaining cakes.