Adapted from Pinch My Salt, which notes that you can use any stout or porter instead of Guinness. I adapted the recipe to use a stand mixer and black cocoa, which is super-dark cocoa. Use the ratio of 1/3 black cocoa with 2/3 Dutch processed cocoa powder in baking. I reduced the amount of sugar and added espresso powder.
Have eggs, yogurt, and stout at room temperature before starting. Yield: 18 cupcakes.
6 Tablespoons butter, melted
2 large eggs, at room temperature
1/2 cup plain, thick yogurt, at room temperature
6 oz. dark stout (I used Guinness), at room temperature
2 teaspoons vanilla extract
2 Tablespoons black cocoa plus enough Dutch processed cocoa powder to make 1/2 cup cocoa total
1 Tablespoon espresso powder
2/3 cup sugar
1-1/4 cups all purpose flour
1 teaspoon baking soda
1/8 teaspoon ground cinnamon
Heat oven to 350 degrees. Line a 12-cup cupcake pan with cupcake papers; spray the whole thing, cupcake papers and all, with nonstick spray. Set aside. (Note: I had enough batter for an additional 6 cupcakes).
Melt butter in microwave or on stovetop, then set aside.
In the bowl of a stand mixer, beat together eggs, yogurt, and vanilla. Add stout; beat until well combined.
Whisk all the dry ingredients together (cocoa powder, espresso powder, sugar, flour, baking soda, and cinnamon) in a separate bowl.
Add the cocoa mixture to the wet ingredients in thirds, beating until well mixed after each addition. When all ingredients are blended, add the melted butter, then continue mixing until very well combined.
Pour batter into the prepared cups, filling each only about 3/4 full.
Bake on center rack of the oven for approximately 25 minutes.
When cupcakes are done (toothpick inserted in center of a cupcake will come out clean), remove the pan to a wire rack. Let cool for ten minutes, then remove cupcakes from pan, and let them cool completely on wire rack.