Notes from the Test Kitchen:
Thanks to the sour cream and buttermilk, these chocolate cupcakes are so moist! The coffee buttercream is fabulous. The flavor of the coffee is subtle and delicious. I'd suggest doubling the coffee buttercream recipe ... you may find yourself eating it by the spoonful.
Preheat oven to 350. Sift flour, cocoa powder, baking soda and salt into a bowl.
In another large bowl, whisk together sugar, egg, oil, sour cream and vanilla until well mixed.
Stir or whisk a third of the dry ingredients into sugar mixture until just mixed. Next stir or whisk in half of the buttermilk until just mixed. Repeat this step ending with the dry ingredients.
Spoon batter into lined cupcake pans 2/3 full. Bake for 17 minutes. Let cool.
For the Coffee Buttercream: Using a stand mixer or hand mixer beat butter and 4 cups of sifted powdered sugar until creamy but stiff. Add coffee and beat until spreading or piping consistency. Should be creamy but stiff enough to pipe or spread and hold shape. You may need to add a little more powdered sugar.
Pipe or spread buttercream onto cooled cupcakes and enjoy.