Buttermilk Whoopie Pies

Whoopie pies are a New England classic, somewhere between a cookie, a cake, and a sandwich. Two soft, pillowy chocolate cake-cookies hug a fluffy marshmallow buttercream in the middle. They originated in Pennsylvania Dutch country and Maine claims them as a state treasure, with both regions having stuck them in lunchboxes for generations.

The buttermilk is what gives these their signature soft, cakey texture. The acid in the buttermilk reacts with the baking soda for an exceptional rise, and the milk fat adds tenderness without weighing down the crumb. Don’t substitute regular milk. The recipe loses its character entirely without that tangy lift.

Drop the batter in even mounds. Whatever shape you drop is what bakes, so take a moment to round each scoop with the back of the spoon. An ice cream scoop with a release lever produces uniform, identical cookies that pair up perfectly later.

Watch the doneness cue: cookies are done when they spring back at a light touch and the tops no longer look shiny. Overbaked whoopie pies turn dry and lose the cushiony bounce that makes them whoopie pies and not hockey pucks.

The marshmallow filling needs the powdered sugar beat in last. Add it gradually with the mixer running. Dumping it in all at once sends a sugar cloud across the kitchen.

Pro Tips

• Cool the cookies completely before filling. Warm cookies melt the marshmallow buttercream into a soggy mess.
• Pair similar-sized cookies together. Sort by size before filling for clean uniform pies.
• Wrap each filled pie individually in plastic wrap for lunchbox-portable storage.
• These freeze well, filled and wrapped, for up to a month.

Variations

• Add a teaspoon of espresso powder to the dry mix for deeper chocolate flavor.
• Swap marshmallow filling for cream cheese frosting for a tangier, less sweet pie.
• Roll the edges of the filled pies in mini chocolate chips or sprinkles.