With soft & cakey chocolate sandwich cakes and an old-fashioned vanilla filling, Gluten-Free Whoopie Pies are everything delicious and nostalgic without any of the wheat products or gluten!
In a large bowl, mix together the melted butter, oil, brown sugar, and instant espresso, if using.
Add one egg at a time, beating after each addition.
Add the buttermilk and vanilla extract and beat until smooth. Set aside.
In a separate bowl, combine the gluten-free flour, cornstarch, cocoa powder, salt, baking soda, and baking powder. Add this mixture to the wet ingredients and stir until smooth. Let this batter rest for 30 minutes.
While the batter rests, preheat the oven to 340°F (170°C) and line a baking sheet with parchment paper.
Scoop the batter using a cookie scoop (about 1½ tablespoons) and place them on the parchment paper leaving 2 inches between.
Bake the cakes for 8 minutes. Let them cool on the baking sheet for 1-2 minutes before taking them off onto a wire rack to cool completely.
Vanilla buttercream frosting
In the bowl of a stand mixer or a large bowl with a hand mixer, beat the butter and shortening until light and fluffy, about 3 minutes.
Add the powdered sugar 1 cup at a time and continue beating. Scrape the sides and bottom of the bowl with a spatula after each addition. Taste to see if it's sweet to your liking. Add more sugar if you'd like.
Add the salt and vanilla and beat again until combined.
Using a piping bag, or a spatula, put some frosting onto the bottom of one cake, and top with another, making a sandwich. Repeat with the rest of the cakes.
Notes
Refrigeration: Leftover whoopie pies keep covered in an airtight container in the refrigerator for 3-4 days.Freezing: The pies can also be frozen in a freezer-safe container for up to 3 months. For best results, wrap the gobs up in parchment paper or plastic wrap before placing in the freezer-safe container. Dairy-Free: To make dairy-free whoopie pies, use vegan butter in place of unsalted butter and substitute dairy-free homemade sour milk for the buttermilk. To make sour milk, add 1 tablespoon of distilled vinegar to a 1-cup measuring cup. Fill the cup with plant milk to the 1-cup line and stir. Let sit for 3-5 minutes and then use the sour milk in place of the buttermilk as directed.