Chocolate Frosting

Chop the chocolate and place it in a heat-proof bowl set over a pan of simmering water. Stir until just melted and set aside until cooled to room temperature.

In the bowl of an electric mixer fitted with a paddle attachment, beat the butter on medium-high speed until light yellow and fluffy, about 3 minutes. Add the egg yolk and vanilla extract and continue beating for 3 minutes. Turn the mixer to low, gradually add the confectioners sugar, then beat at medium speed, scraping down the bowl as necessary, until smooth and creamy. Dissolve the coffee powder in 2 tsp of hot tap water. On low speed, add the chocolate and coffee to the butter mixture and mix until blended. Don't whip. Spread immediately on cooled cakes or cupcakes.