2 cups (240g) all-purpose flour
1/2 (42g) cup Dutch-process cocoa powder
1 1/4 tsp baking soda
1 tsp salt
1 cup (240g) well-shaken buttermilk
1 tsp vanilla
1 stick (1/2 cup) unsalted butter, softened
1 cup (213g) packed brown sugar
1 large egg
1/4 cup (46g) vegetable shortening
1/4 cup (57g) unsalted butter, room temperature
1 cup (115g) powdered sugar
1 1/2 teaspoons pure vanilla extract
1/4 cup (78g) light corn syrup
Preheat oven to 350°F. Pull out 2 large baking sheets pans, line with parchment paper or butter them.
In medium sized bowl, whisk together flour, cocoa, baking soda & salt.
In liquid measuring cup or small bowl, stir together buttermilk and vanilla.
Using electric mixer with paddle attachment, cream together butter & brown sugar on medium-high speed until pale and fluffy. Add egg, beating until combined.
Reduce mixer speed to low and alternately mix in flour mixture and buttermilk in batches, beginning and ending with flour, scraping down side of bowl occasionally, and mixing until smooth.
Spoon 1/4-cup mounds of batter about 2 inches apart onto your buttered baking sheets (best if use cookie scoop).
Bake in upper and lower thirds of oven, switching position of sheets halfway through baking, until tops are puffed and cakes spring back when touched, 11 to 13 minutes.
Transfer with a metal spatula to a rack to cool completely.
Using electric mixer with paddle attachment cream the shortening and butter until soft and creamy.
Reduce mixer speed to low, gradually mix in the confectioners' sugar. Increase the speed to high, and beat until light and fluffy, about 3-5 minutes.
Return mixer to low speed, beat in the vanilla extract and slowly drizzle in the corn syrup.
Increase mixer speed and beat until filling in spreadable but firm enough to stay put.
Make sure cookies are completely cooled before assembling. Spread about 3 tbsp (or more) of filling on to the bottom of one cookie and sandwich with another. Continue sandwiching all whoopie pies. Enjoy.