The cake I wound up with is quite possibly the best cake I have ever made. It has both bittersweet chocolate and dark chocolate cocoa powder in it, which together create a deep, decadent, but not overly sweet, chocolate flavor. The sour cream adds a moistness and subtle tang, and the coconut extract and flaked coconut are out of this world.
The frosting is somewhat of a different story. I attempted to make a simple coconut icing based on a recipe in one of my cookbooks. As I discovered halfway through making it, however, the recipe must have been misprinted - there was no thickening agent. So I haphazardly added cornstarch and a few other ingredients in an attempt to save it...needless to say, it was not the best frosting I have ever made. It turned out hard, almost like a coconut candy. Delicious, but not the best for icing a cupcake. And so I haven't included that recipe (if you can call it that) in this post. I'd recommend you frost these with a vanilla buttercream - something light and sweet and subtle enough to let the cake really shine.
2 ounces bittersweet chocolate, chopped
1/2 cup dutch-processed cocoa powder
3/4 cup all-purpose flour
1/2 teaspoon baking soda
1/4 teaspoon baking powder
¾ cup granulated sugar
1 teaspoon coconut extract
1/2 teaspoon vanilla extract
1/2 teaspoon kosher salt
1/2 cup (4 ounces) sour cream
1/2 cup sweetened flaked coconut
adjust oven rack to lower-middle position and preheat to 350 degrees. (if using a non-stick muffin pan, heat the oven to 325 degrees.) Line muffin pan with baking cup liners.
combine butter, chocolate, and cocoa in medium heatproof bowl. set bowl over saucepan of barely simmering water; heat mixture until butter and chocolate are melted and whisk until smooth and combined. set aside to cool until just warm to the touch.
whisk flour, baking soda and baking powder in small bowl to combine. whisk eggs in second medium bowl to combine. add sugar, vanilla, coconut extract, and salt until fully incorporated. add cooled chocolate mixture, whisk until combined.
sift about 1/3 of flour mixture over chocolate mixture and whisk until combined, then whisk in sour cream. sift in remaining flour mixture and whisk until batter is homogeneous and thick. add in the flaked coconut and stir until well-combined.
divide the batter evenly among muffin cups. bake until toothpick inserted into center of cupcakes comes out clean, about 20 minutes.
cool cupcakes in muffin pan on wire rack until cool enough to handle, about 10 minutes, then transfer each cupcake to cooling rack. cool to room temperature before icing.