Preheat your oven to 350°F (175°C). Line two large baking sheets with parchment paper. This keeps the cakes from sticking and makes cleanup quick—just the way Grandma liked it.
In a medium bowl, whisk together the flour, cocoa powder, baking soda, baking powder, and salt until well combined. Set aside; this will be your dry mixture.
In a large mixing bowl, beat 1/2 cup softened butter and the granulated sugar together with a hand mixer (or a sturdy wooden spoon) until light and creamy, about 2-3 minutes. The mixture should look a bit fluffy.
Beat in the eggs, one at a time, mixing well after each addition. Stir in 1 teaspoon vanilla extract.
Add the dry mixture to the wet mixture in two additions, alternating with the 1 cup of milk. Start with half the dry ingredients, mix gently, pour in half the milk, then repeat. Stir just until the batter is smooth and no dry streaks remain; don’t overmix or the cakes can get tough.
Using a tablespoon or a small cookie scoop, drop rounded spoonfuls of batter onto the prepared baking sheets, spacing them about 2 inches apart. Aim for 20–24 mounds total so you’ll have enough to make 10–12 sandwiches.
Bake one sheet at a time in the preheated oven for 8–10 minutes, or until the tops spring back lightly when touched and a toothpick inserted in the center of a cake comes out clean or with just a few moist crumbs.
Let the cakes cool on the baking sheet for about 5 minutes, then transfer them carefully to a wire rack to cool completely. The filling will melt if the cakes are warm, so give them time.
While the cakes cool, make the filling. In a medium bowl, beat 1/2 cup softened butter until smooth and creamy. Gradually add the powdered sugar, mixing on low at first so it doesn’t puff everywhere.
Stir in 2 tablespoons of milk, 1 teaspoon vanilla extract, and a pinch of salt. Beat until the filling is thick, smooth, and spreadable. If it seems too stiff, add up to 1 more tablespoon of milk, a few drops at a time; if it’s too soft, beat in a little more powdered sugar.
To assemble, turn half of the cooled cakes flat-side up. Spoon or pipe a generous tablespoon of filling onto each. Top with the remaining cakes, flat-side down, and gently press to spread the filling to the edges so it just peeks out.
Arrange the finished whoopie pies on a ceramic platter and serve, or chill them for 30–60 minutes to set the filling. Store leftovers in an airtight container in the refrigerator for up to 3 days, bringing them to room temperature before serving for the best texture.
Variations & Tips
