1/2 cup salted butter, softened at room temperature
1 cup light brown sugar, packed (220 grams)
1 large egg, at room temperature
1 tsp vanilla extract
1 cup buttermilk (236 mL)
2 cups + 2.5 tbsp all-purpose flour, spooned & leveled or weighed out (280 grams)
1/3 cup + 2 tbsp, cocoa powder (37 grams)
1/4 tsp salt
1 and 1/4 tsp baking soda
1/4 cup salted butter, softened at room temperature
2 cups powdered sugar (230 grams)
1-2 tbsp milk
1 tsp vanilla extract
pinch of salt
4 oz cold cream cheese, cubed
Instructions:
Prep: Preheat the oven to 350℉. Line a few cookie sheets with parchment paper and set aside.
Make the Whoopie Pie Batter: In a large mixing bowl, cream the softened butter with a mixer until smooth. Add the brown sugar and beat until completely combined and fluffy, about 2 minutes. Add the egg and vanilla, and mix on medium-high speed until combined and fluffy, about 1 minute.In a smaller mixing bowl, whisk together the flour, cocoa powder, salt, and baking soda. Alternate adding the milk and the dry ingredients in thirds to the bowl with the butter/sugar mixture. So, add 1/3 of the dry mixture, and then mix on low speed until it's almost all mixed in, then do the same with the milk. Repeat until everything is mixed in and stop mixing just as the last streaks of flour and milk disappear. Use a spatula to gently scrape the sides and bottom of the bowl to make sure everything is incorporated - it's important not to overmix! The batter will be thinner than cookie dough but a little thicker than cake batter.
Bake: Drop a cookie scoop or a heaping tablespoon full of batter onto the parchment paper on your prepared baking sheets, leaving about 3 inches in between each batter blob. Don't flatten them at all! You can fit about 8 batter blobs on a cookie sheet at a time. Bake one cookie sheet at a time - for 9 minutes. To check if they're done, gently poke one of the cookies with your finger - if it makes a dent, it could use another minute or two. If the cookie springs back, it's done. Also, a toothpick inserted into the center should pull out moist crumbs, not batter. Allow the whoopie pies to cool on the baking sheet set on a wire rack until cool enough to handle, then let them cool completely on the wire rack (without the pan) before frosting.
Make the Frosting: While the whoopie pie cookies are baking, make the frosting. Cream the softened butter in a large bowl for about 1 minute, or until creamy. Add all frosting ingredients except the cream cheese, and mix until smooth. Add a little more milk as needed to help things come together. Beat in the cubed cold cream cheese last. This prevents the frosting from becoming runny.
Assemble: When the cookies are completely cooled, spread half of them with frosting, and add the second piece on top to make a whoopie pie. Try to pair the cookies up based on similar size for a neat look. Dust with powdered sugar if desired. Enjoy right away!
Store: Store leftover whoopie pies in an airtight container in the fridge for 3-4 days.
Make-Ahead Tips: Frosting can be made up to 2 days ahead and refrigerated. When ready to use, allow to sit at room temperature for 15-20 minutes, then mix with the mixer again to get it back to a spreadable consistency.