Preheat oven to 450F (235C) and line several cookie sheets with parchment paper³. Set aside.
In a large bowl or in the bowl of a stand mixer, combine sugar and shortening and beat together until well-combined. 1 cup (200 g) sugar, ¼ cup shortening
Add egg and vanilla extract and stir until mixture is pale yellow and well-combined.1 large egg, 1 teaspoon vanilla extract
Stir in buttermilk and then set mixture aside.½ cup (120 ml) buttermilk¹
In a separate, medium-sized bowl, whisk together flour, cocoa powder, baking soda, baking powder, and salt. Prepare your boiling water.2 cups (250 g) all-purpose, ¼ cup (50 g) cocoa powder², 1 teaspoon baking soda, ¼ teaspoon baking powder, ½ teaspoon salt, ½ cup (120 ml) very hot or boiling water
Alternate adding the dry ingredients and hot/boiling water to the wet ingredients, starting and ending with the dry ingredients and stirring until combined after each addition. I usually add the flour in 3 parts and the water in 2.
Stir until well-combined and mixture is smooth. Be sure to use a spatula to scrape the sides and bottom of the bowl to ensure ingredients are thoroughly combined. The mixture should be thin like a cake batter rather than thick like a cookie dough.
Drop cookie batter by a heaping Tablespoon onto prepared baking sheets, spacing cookies at least 2” apart (they will spread in the oven).
Bake for 5 minutes in 450F (235C) oven, then remove from oven and allow to cool completely.
Meanwhile, prepare your cream filling.
FILLING
This Whoopie Pie filling starts with a flour/milk paste that’s critical to the texture and consistency of an old-fashioned Whoopie Pie/Gob. Pour milk into medium-sized saucepan over medium/low heat and then sift/whisk flour into milk until smooth.1 cup (236 ml) whole milk, 5 Tablespoons all-purpose
Continue to whisk constantly until mixture is thickened to a near paste-like consistency that wants to cling together. Remove from heat and allow to cool completely, stirring occasionally to prevent a skin from forming, before proceeding (if it’s warm and you proceed you’ll melt your filling and have a runny mess). If you refrigerate the filling, press a piece of plastic wrap directly against the surface to prevent a skin from forming. To speed up the process you can pour mixture into another container but it will take at least 30 minutes. Flour mixture will thicken even more as it cools.
Once flour/milk mixture has cooled, add to a medium-sized mixing bowl along with butter, shortening, salt and vanilla. Use an electric mixer to beat until creamy and well-combined.¾ cup (170 g) unsalted butter, 2 Tablespoons shortening, ¼ teaspoon salt, 1 teaspoon vanilla extract
With mixer on low speed, gradually add powdered sugar until completely combined.1 cup (125 g) powdered sugar
Pair up your cooled chocolate cookies so that you have evenly-sized pairs.
Pipe or spread filling onto the bottom of one cookie then top with another cookie to make a sandwich. Repeat until all cookies are filled. Enjoy!