Mocha Buttercream

Preparation

1. Step 1

   In a small bowl, combine the espresso powder with the hot water, and stir until dissolved; set aside. In a heatproof bowl set over a pan of simmering water, whisk together the egg whites and sugar until the sugar is dissolved, and the mixture is warm to the touch, 2 to 3 minutes.

   Step 2

   In the bowl of an electric mixer fitted with the whisk attachment, beat the egg-white mixture on high speed until slightly cooled and stiff, and glossy (but not dry) peaks have formed, about 6 minutes.

   Step 3

   Switch to the paddle attachment. With the mixer on medium-low speed, add the butter, several tablespoons at a time, beating well after each addition (the mixture will deflate slightly as butter is added). Continue beating until smooth and fluffy, 3 to 5 minutes. (If the frosting appears to separate after all the butter has been added, beat on medium-high speed until smooth again.) With the mixer on low speed, add the chocolate, then the espresso mixture; beat until smooth, about 1 minute. Beat on the lowest speed to eliminate any air bubbles, about 2 minutes. Cover with plastic wrap, and refrigerate until ready to use.