- 1 stick unsalted butter, cut into 4 pieces
- 2 ounces bittersweet chocolate, chopped
- ½ cup Dutch-processed cocoa powder
- ¾ cup all-purpose flour
- ½ teaspoon baking soda
- 2 eggs
- ¾ cup granulated sugar or Splenda brand sweetener
- 1 teaspoon vanilla extract
- ½ cup sour cream
1. Adjust oven rack to lower-middle position and preheat to 350 degrees F. (If you are using a non-stick muffin pan, heat the oven to 325 degrees F.) Line standard-size muffin pan with baking cup liners.
2. Combine butter, chocolate, and cocoa in medium heatproof bowl. Microwave the mixture at 50% power, stirring every 30 seconds until completely melted. Set aside to cool until just warm to the touch.
3. Sift flour and baking soda in a small bowl.
4. Whisk eggs in second medium bowl to combine; add sugar (or Splenda) and vanilla until fully incorporated. Add cooled chocolate mixture and whisk until combined. Add one-third of flour mixture into the chocolate mixture and whisk until combined; whisk in sour cream until combined, whisk until batter is thick.
5. Divide the batter evenly among muffin pan cups. Bake until skewer inserted into center of cupcakes comes out clean, 18 to 20 minutes.
6. Cool cupcakes in muffin pan on wire rack until cool enough to handle. Carefully lift each cupcake from muffin pan and set on wire rack. Cool to room temperature before icing.
For the Vanilla Buttercream Frosting
- 1 cup (8 ounces) unsalted butter, at room temperature
- 2½ cups powdered sugar
- 1 tablespoon vanilla extract
1. Using the wire whisk attachment of your stand mixer, whip the butter on medium-high speed for 5 minutes, stopping to scrape the bowl once or twice.
2. Reduce the speed to low and gradually add the powdered sugar. Once all of the powdered sugar is incorporated, increase the speed to medium-high and add the vanilla, mixing until incorporated. Whip at medium-high speed until light and fluffy, about 2 minutes, scraping the bowl as needed.