Everybody eats whoopee cakes, but do you know how to make them? Here is the original recipe, from kingarthurflour.net, as printed in our Baker’s Catalogue. It yields a very assertively flavored mocha cake with dark chocolate ganache filling.
Let’s start by making the cakes. Beat together the following until smooth:
Preheat the oven to 350°F. Lightly grease two baking sheets, or line with parchment.
1/2 cup (8 tablespoons) butter, at room temperature
1 cup brown sugar
2 to 3 teaspoons espresso powder, to taste*
1 teaspoon baking powder
1/2 teaspoon baking soda
3/4 teaspoon salt
*For plain chocolate whoopie pies, eliminate the espresso powder.
Though the original recipe doesn’t call for it, I like to add 1 teaspoon vanilla. Like a small amount of espresso powder, vanilla highlights chocolate’s flavor without adding any assertive taste of its own.
Add 1 large egg, again beating until smooth.
Stir in 1/2 cup Dutch-process cocoa. I’m using our King Arthur all-purpose baking cocoa, which I feel combines the best of both natural and Dutch-process cocoas. Which makes total sense – since it’s a blend of the two, plus black cocoa, as well.
Add 2 1/3 cups (9 5/8 ounces) King Arthur Unbleached All-Purpose Flour alternately with 1 cup milk. First some flour; mix it in; then some milk, mix it in. Maybe a heaping 1/2 cup flour and 1/3 cup milk at a time.
Once everything is added beat until smooth, scraping down the sides and bottom of the bowl to make sure any pasty ingredients are fully incorporated.
Drop the dough by the heaping tablespoonful onto the baking sheets. A tablespoon cookie scoop works very well here.
Leave about 1 1/2″ to 2″ between the rounds, as they’ll spread a bit.
You’ll need to bake the cakes in batches, as you can bake maybe 2 dozen at a time, and the recipe makes about 32 cakes (and therefore about 16 whoopie pies).
Mix the following in a microwave-safe bowl, or a saucepan:
2 cups (1 pint) heavy or whipping cream
1 bag (10 to 10 1/2 ounces) marshmallows; mini-marshmallows are easiest to use
1 cup confectioners’ sugar
1/8 teaspoon salt
Next, decide your chosen level of coffee flavor. I opted for using 2 teaspoons of espresso powder; if you don’t have espresso powder, try instant coffee powder, or instant coffee granules dissolved in a tiny bit of water.
Heat gently, stirring frequently, until the marshmallows melt completely.
Remove from the heat, and stir in 1 teaspoon vanilla.
Pour the icing into the bowl of your stand mixer or another mixing bowl, and refrigerate until chilled.
Once the icing is thoroughly chilled, beat at high speed using your stand mixer or an electric hand mixer; it’s impossible to whip fully by hand, so please use a machine. Scrape the sides and bottom of the bowl to make sure you’re incorporating all of the chilled icing.
As you beat it the icing will warm up, expanding in volume and lightening in color. Be sure to beat long enough for this to happen, and for the icing to become very smooth.
Spread the flat side of half the cakes with the filling. It helps to dollop it on with your trusty tablespoon cookie scoop, then gently spread nearly to the edge of the cake.
Top with the remaining cakes, rounded side up; press down gently