• Preheat the oven to 375° F. Line a cookie sheet with parchment paper or a silicone baking mat.
• In the bowl of a stand mixer or with an electric hand mixer, combine the softened butter and brown sugar until combined.
• Add the egg and vanilla, mixing well.
• Add the flour, black cocoa powder, cornstarch, baking soda and salt to the bowl. Slowly start mixing. As the dry ingredients are mixing in, slowly add in the buttermilk and finish with the black food coloring.
• Mix until a thick batter forms.
• Add the batter to a piping bag. Pipe round circles equal in size onto the prepared baking sheet, leaving room for the cookies to bake and spread. Alternatively you can scoop the batter onto the pan.
• Bake at 375° F for 8-10 minutes or until the cookies have spread and no longer look wet and underbaked in the center of the cookie.
• Allow the cookies to cool on the pan.
• While the cookies are cooling, make the filling.

Buttercream Filling

• To make the filling, slowly cream the butter until smooth.
• Add powdered sugar one cup at a time, adding a splash of heavy cream to the bowl with it to help incorporate the powdered sugar into the butter.
• Repeat the last step until all 3 cups of powdered sugar have been added.
• Add in the clear vanilla extract and more heavy cream to thin the filling, if needed.
• If coloring your frosting, add in your desired food coloring.
• Add the filling to a piping bag. Pipe the filling onto the bottom of a cooled chocolate cookie and top it with another cookie to create the whoopie pie. Repeat with remaining cookies!
• Store in an airtight container for up to 3 days at room temperature or up to 1 week in the fridge. Enjoy!