Ganache Filling:
Place chocolate, cream, and confectioners' sugar in medium microwave-safe bowl. Heat in microwave until mixture is warm to touch., 20-30 seconds. Whisk until smooth; transfer bowl to refrigerator and let stand until just chilled, no longer than 30 minutes.
Cupcakes:
adjust oven rack to middle position and heat oven to 350 degrees. Line standard-size muffin pan (cups have 1/2 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.
Whisk oil, eggs, vinegar, and vanilla into cooled chocolate-cocoa mixture until smooth. Add flour mixture and whisk until smooth.
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 the touch, 17-19 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. Frost and serve.
Swiss Chocolate meringue buttercream Frosting:
Combine sugar, egg whites, and salt in bowl of stand mixer; place bowl over pan of simmering water. Whisking gently but constantly, heat mixture until slightly thickened, foamy, and registers 150 degrees on instant-read thermometer, 2-3 minutes.
Place bowl in stand mixer fitted with whisk attachment. Beat mixture on medium speed until consistency of shaving cream and slightly cooled, 1-2 minutes.
Add butter, 1 piece at a time, until smooth and creamy. Once all butter is added, add cooled and melted chocolate and vanilla; mix until combined.
Increase speed to medium-high and beat until light, fluffy, and thoroughly combined, about 30 seconds, scraping beater and sides of bowl with rubber spatula as necessary. Place finished frosting in microwave 5-10 seconds and stir 'til creamy if it becomes too thick to spread (if made in advance.)
VARIATIONS:
Creamy Malted Milk Chocolate Frosting:
Follow recipe for Creamy Chocolate Frosting, reducing sugar to 1/4 cup, substituting milk chocolate for bittersweet chocolate, and adding 1/4 cup malted milk powder to frosting with vanilla extract in step 2.
Creamy Vanilla Frosting:
Follow recipe for Creamy Chocolate Frosting, omitting bittersweet chocolate and increasing sugar to 1/2 cup. (if final frosting seems too thick, warm mixer bowl briefly over pan of simmering water. Place bowl back on mixer and beat on medium-high until creamy.)
Creamy Peanut Butter Frosting:
Follow recipe for Creamy Chocolate Frosting, omitting bittersweet chocolate, increasing sugar to 1/2 cup and increasing salt to 1/8 tsp. Add 2/3 cup creamy peanut butter to frosting with vanilla extract in step 2. Garnish cupcakes with 1/2 cup chopped peanuts.
Creamy Butterscotch Frosting:
Follow recipe for Creamy Chocolate Frosting, substituting dark brown sugar for granulated sugar and increasing salt to 1/2 tsp
