How to Make It
Preheat the oven to 325°. Line 24 muffin cups with paper liners. Lightly spray the paper liners with vegetable oil spray. In a small bowl, mix the chocolate and 1/4 cup of cocoa. Add the boiling water and let melt, then whisk until smooth. In a medium bowl, whisk the flour with the baking soda and salt. In a large bowl, using an electric mixer, beat the butter and brown sugar until fluffy. Beat in the eggs, buttermilk and vanilla, then slowly beat in the dry ingredients and the chocolate mixture in 3 alternating batches.
Fill the muffin cups three-fourths full with the batter. Bake for 22 to 25 minutes, shifting the pans halfway through, until the cupcakes are springy and a toothpick inserted in the center comes out with a few moist crumbs attached. Let the cupcakes cool in the pans for 15 minutes, then unmold them and transfer to a rack to cool completely.
Mix the egg whites, confectioners' sugar and 1 teaspoon of espresso in a medium stainless steel bowl. Set the bowl over a saucepan of simmering water and heat the whites, whisking constantly, until hot to the touch (165°). Transfer the mixture to the bowl of a standing electric mixer fitted with a whisk and beat at high speed until the meringue is stiff and glossy, about 5 minutes; if using a handheld mixer, beat for about 8 minutes.
Scoop half of the espresso meringue into a pastry bag fitted with a large (3/4-inch) plain tip and pipe the meringue onto half of the cupcakes. Repeat with the remaining espresso meringue and cupcakes. Lightly sprinkle the meringue with cocoa and espresso powder and serve.