8 Tb unsalted butter, cut into 4 pieces
2 oz. bittersweet chocolate, chopped
½ cup Dutch processed cocoa
¾ cup unbleached all-purpose flour
½ teaspoon baking soda
¾ teaspoon baking powder
2 large eggs
¾ cup sugar
1 teaspoon vanilla extract
½ teaspoon table salt
½ cup sour cream
VANILLA BEAN BUTTERCREAM INGREDIENTS:
10 Tb unsalted butter, softened
½ vanilla bean, halved lengthwise (if you don’t have a vanilla bean, increase the vanilla extract to 1½ teaspoons)
1¼ cups confectioners’ sugar
pinch of table salt
½ teaspoon vanilla extract
1 Tb heavy cream
Place oven rack in middle position, preheat oven to 350 degrees F. Line standard-sized muffin pan with cupcake liners.
Combine butter, chocolate, and coca powder in medium heatproof bowl. Set over a saucepan of simmering water. Heat mixture until butter and chocolate are completely 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 (or standing mixer) to combine, add sugar, vanilla and salt and whisk until fully incorporated. (Here I use a standing mixer and the paddle attachment). Add cooled chocolate mixture and whisk until combined. Sift about one-third of the flour mixture over the chocolate mixture and whisk until combined. Whisk in sour cream until combined. Then sift remaining flour mixture over and whisk until homogenous and thick.
Divide batter evenly among muffin pan cups. Bake 18 – 20 minutes.
Cool cupcakes in muffin pan on wire rack until cool enough to handle, about 15 minutes. Carefully lift each cupcake from the muffin pan and set on a wire rack to cool completely, about 30 minutes. Frost with icing when the cupcakes are at room temperature.
VANILLA BEAN BUTTERCREAM DIRECTIONS:
In standing mixer fitted with whisk attachment, beat butter at medium-high speed until smooth, about 20 seconds. Using a paring knife, scrape the seeds from the vanilla bean into the butter and beat mixture at medium-high speed to combine, about 15 seconds.
Add confectioners’ sugar and salt. Beat at medium-low speed until most of the sugar is moistened, about 45 seconds. Scrape down bowl and beat at medium speed until mixture is fully combined, about 15 seconds.
Scrape bowl, add vanilla and heavy cream, and beat at medium speed until incorporated, about 10 seconds. Increase speed to medium-high and beat until light and fluffy, about 4 minutes, scraping down the bowl once or twice.