For the Sandwich Cookies:
- 2 cups all-purpose flour
- 2/3 cup cocoa powder
- 1 1/4 teaspoons baking soda
- 1 teaspoon salt
- 1 cup buttermilk
- 1 teaspoon vanilla extract
- 8 tablespoons butter, softened
- 1 cup brown sugar, packed
- 1 large egg, whole
For the Peanut Butter Filling:
- 1/2 cup unsalted butter, room temperature
- 1/2 cup creamy peanut butter, room temperature
- 1/4 cup granulated sugar
- 1/2 teaspoon vanilla extract
- 2 tablespoons heavy whipping cream, cold
- For the Sandwich Cookies: Preheat oven to 350°F.
- Sift together flour, cocoa, baking soda and salt in a medium bowl. Set aside.
- Stir together buttermilk and vanilla in a small bowl. Set aside.
- In an electric mixer fitted with the paddle attachment, add butter and brown sugar. Cream on medium speed until pale and fluffy, about 2 minutes.
- Add the egg and beat to incorporate. Scarping down bowl and beating again to insure all ingredients are incorporated and not lumpy.
- Reduce speed to low and alternately mix in flour mixture and buttermilk mixture in batches, beginning and ending with flour, scraping down sides of bowl and mix until smooth.
- Use a 1 ounce or 1.25 ounce cookie scoop, scoop dough into greased whoopie pie specialty pan and bake at 350°F until puffed and cakes spring back when touched, 9-10 minutes.
- For the Peanut Butter Filling: In an electric mixer fitted with the paddle attachment add butter, peanut butter and sugar. Beat ingredients on medium-high speed until fluffy and lump free, 2 to 3 minutes.
- Change out the paddle attachment to the whisk attachment; reduce speed to low, add vanilla. Mix until fully incorporated.
- With the mixer running in medium speed, add in the heavy cream, turn to high speed and whip until medium to stiff peaks form.
- Fill cooled whoopie pies with 1 tablespoon of filling.