6oz.dark or semi-sweet chocolate melted and slightly cooled
¼cup+ 2 tablespoon Dutch process cocoa powdersifted
For the Dark Chocolate Cupcakes
Preheat oven to 350 degrees and line a standard cupcake pan with 12 cupcake liners.
Start by creaming together the butter and sugar in a large bowl with an electric mixer.
Then add in the egg, egg yolk and vanilla and mix until pale and fluffy, about 1 minute.
Next mix in the milk and sour cream.
In a small bowl whisk together the flour, cocoa powder, baking powder, baking soda, salt and espresso powder.
Add the dry ingredients to the wet ingredients and mix until the batter is smooth.
Fill each cupcake liner ¾ of the way full.
Bake the cupcakes for 17-20 minutes, or until a toothpick/cake tester comes out clean from the centers.
Let the cupcakes cool in the pan for 5 minutes then transfer to a cooling rack to cool completely.
For the Dark Chocolate Buttercream
While the cupcakes are cooling make the frosting by adding the softened, unsalted butter and salt to a medium sized bowl. Mix with an electric mixer until the butter is pale in color and fluffy, about 5-10 minutes.
Add in the melted and slightly cooled dark chocolate and combined.
Next add in the sifted Dutch process cocoa powder. Mix until combined.
Then add in the sifted powdered sugar a little at a time until it is all combined. The frosting will be thick at this point.
Add in the heavy cream, a tablespoon at a time. Mix until the frosting is light and fluffy, about 1-2 minutes. (Add the heavy cream as necessary. If the frosting is light and fluffy after only two tablespoons, don't add the full amount. If it's still too dry after 3 tablespoons, add more.)
Assembling the Cupcakes
Once the cupcakes are cool, add the dark chocolate buttercream to a large piping bag fitted with a decorative tip.
Pipe a generous amount of frosting onto the tops of each cupcake. Serve right away.
Store left overs in an airtight container in the fridge for up to three days. Let the cupcakes come to room temperature before enjoying so the frosting has a chance to become soft again.