Old-Fashioned Whoopie Pie

Why This Old-Fashioned Whoopie Pie Works

In the oven, the cocoa batter puffs up like little cakes instead of spreading flat. Butter and sugar beaten together trap tiny air pockets, and the baking soda expands those pockets when it hits the heat. At the same time, the flour and eggs set up a soft structure so the rounds hold their shape but still stay tender. Buttermilk keeps the batter loose enough to drop, but its acid also reacts with the baking soda, so the cakes rise instead of baking up dense.

As the cakes cool, they firm up just enough so they can be picked up without breaking. Cooling also keeps the filling from melting out. In the bowl, the butter and powdered sugar for the filling whip full of air and turn thick and fluffy. Marshmallow creme gives that stretchy, pillowy feel and helps the filling stay put between the cakes. Once sandwiched, the soft chocolate cakes and the fluffy center press together and hold as one piece, but still bite through easily.

Mistakes To Avoid

Overbaking the cakes easily turns them dry and crumbly. Once they go past the “spring back when touched” stage, the edges harden and the centers lose their soft, cake-like texture, so the whoopie pies feel tough instead of pillowy when bitten.

Adding all the buttermilk at once instead of alternating with the dry mix often makes the batter lumpy and uneven. Dry pockets of flour can stay in the mix while other parts get overmixed and tight, which leads to flat, uneven cakes in the oven.

Using warm cakes for filling causes trouble fast. The heat softens the butter and marshmallow filling until it loosens and starts to ooze out the sides, and the top cake can slide around instead of staying stacked.

Beating the filling too little leaves tiny lumps of butter and powdered sugar. Those lumps don’t smooth out later, so the center feels grainy and uneven instead of fluffy and light between the cakes.