No photographic evidence because a)I procrastinated snapping a picture, and b)they were eaten too quickly. This is modified from a recipe in the Best of America's Test Kitchen (2008) cookbook, which is for a layer cake.
Yield: about 16 cupcakes
12 tablespoons unsalted butter
2 1/4 cup unbleached all-purpose flour
1 1/2 teaspoons baking soda
1 cup buttermilk
1 tablespoon white vinegar
2 large eggs
2 tablespoons natural cocoa powder (yes, substituting Dutch process is a bad idea)
2 tablespoons (one 1 oz. bottle) red food coloring
1.5 cups (10.5 oz) granulated sugar
Cupcake or muffin liners
1 stick/8 oz. butter
2 cups confectioners' sugar
8 oz. cream cheese (1 package of Phildelphia), cut into 8 pieces and softened
1.5 teaspoons vanilla extract
At least an hour before starting; Take enough butter for both cake and frosting out of fridge or freezer to make sure it softens up enough. Cold butter doesn't blend well with sugar, and there is nothing more disappointing than good cakes ruined by annoying pockets of butter. Note that the exact opposite is true for making pie crust.
1. Preheat oven to 350 degrees. Prepare cupcake pans with liners.
2. Whisk flour, baking soda, and salt together in a medium bowl. Whisk buttermilk, vinegar, vanilla, and eggs together in a medium bowl. Mix the cocoa and food coloring in a small bowl until smooth paste forms.
3. Beat the butter and granulated sugar together on medium high speed in a large bowl until fluffy, about three minutes. Scrape down sides of bowl as needed. (If you have a stand mixer, this is a really good recipe to use it for. I did make a variation of this with a hand mixer in my old apartment and it tasted great, but flour spattered all over the place.) Add one-third of flour mixture and beat on medium-low speed until just incorporated, about 30 seconds. Add half of the buttermilk mixture and beat on low speed until combined, about 30 seconds. Scrape down the sides of the bowl. Repeat, ending with the flour mixture. Scrape down the sides of the bowl, add the cocoa mixture, then mix on medium speed until completely incorporated, about 30 seconds. Using a rubber spatula, give the batter a final stir.
4. Spoon into cupcake liners so that each is about 2/3 full. Bake about 20-25 minutes. (N.b. that the original recipe calls for 25 minutes for the layer cake version.)
FROSTING: With an electric mixer (see above about the hand vs. stand mixer quandary), beat the butter, confectioners' sugar, and salt on medium-high speed in large bowl until fluffy, about 3 minutes, scraping down the sides of the bowl as needed. Add the cream cheese, one piece at a time, and beat until incorporated, about thirty seconds. Beat in the vanilla. Refrigerate until ready to use.