Soft, cake-like whoopie pies sandwiched with fluffy cream filling are a beloved New England family treat. These iconic handheld desserts are part cookie, part cake, and completely irresistible.
Preheat oven to 350°F and line two baking sheets with parchment paper for even heat distribution.
In a large bowl, whisk together flour, cocoa powder, baking soda, baking powder, and salt to thoroughly combine dry ingredients.
In a separate bowl, cream the butter and granulated sugar on medium speed for 3 minutes until light and fluffy, then beat in eggs one at a time, followed by vanilla.
With mixer on low, add half the dry ingredients to the wet mixture, then add milk, then the remaining dry mix; mix until just combined, scraping down the bowl as needed.
Drop rounded tablespoons of batter onto prepared sheets, spacing at least 2 inches apart. Bake for 10–12 minutes until tops spring back. Cool completely before filling.
For the filling, beat vegetable shortening, marshmallow creme, and powdered sugar on high speed for 2 minutes until light and fluffy.
Spread or pipe a generous layer of the filling onto the flat side of half the cakes, then top each with a second cake to create sandwiches.
Let assembled whoopie pies set at room temperature for 30 minutes to allow the filling to firm up before serving.