INSTRUCTIONS
[FOR GANACHE FILLING]
1. Place chocolate, cream, and confectioners' sugar in medium microwave-safe bowl. Heat in microwave on high power until mixture is warm to touch, 20 to 30 seconds. Whisk until smooth; transfer bowl to refrigerator and let stand until just chilled, no longer than 30 minutes.
[FOR CUPCAKES]
2. Adjust oven rack to middle position and heat oven to 350 degrees. Line standard-size muffin pan (cups have ½-cup capacity) with baking-cup liners. Place chocolate and cocoa in medium bowl. Pour hot coffee over mixture and whisk until smooth. Set in refrigerator to cool completely, about 20 minutes. Whisk flour, sugar, salt, and baking soda together in medium bowl; set aside.
3. Whisk oil, eggs, vinegar, and vanilla into cooled chocolate-cocoa mixture until smooth. Add flour mixture and whisk until smooth.
4. Divide batter evenly among muffin pan cups. Place one slightly rounded teaspoon ganache filling on top of each cupcake. Bake until cupcakes are set and just firm to touch, 17 to 19 minutes. Cool cupcakes in muffin pan on wire rack until cool enough to handle, about 10 minutes. Carefully lift each cupcake from muffin pan and set on wire rack. Cool to room temperature before frosting, about 1 hour.
[FOR CREAMY CHOCOLATE FROSTING]
5. Combine the sugar, egg whites, and salt in the bowl of a standing mixer, then place the bowl over a pan of simmering water. Heat the mixture, whisking gently but constantly, until slightly thickened and foamy and it registers 150 degrees on an instant-read thermometer, 2 to 3 minutes.
6. Using the whisk attachment, beat the mixture on medium speed in a standing mixer until it reaches the consistency of shaving cream and is slightly cooled, 1 to 2 minutes. Add the butter, 1 piece at a time, until smooth and creamy. (The frosting may look curdled after half of the butter has been added; it will smooth with additional butter.) Once all the butter is added, add the cooled melted chocolate and the vanilla and mix until combined, about 30 seconds, scraping the beater and sides of the bowl with a rubber spatula as necessary. If, after you add the chocolate, the frosting seems too soft, chill it briefly and then re-whip until creamy.
7. (The frosting can be made up to 24 hours in advance and refrigerated in an airtight container. When ready to frost, place the frosting in a microwave-safe container and microwave briefly until just softened, 5 to 10 seconds. Once warmed, stir until creamy.)
