½cup(43g)cocoa powder, Dutch-process or regular unsweetened
½cuphot water
2 ¼cups(320g)all-purpose flour
¾teaspoonbaking soda
¾teaspoonbaking powder
½teaspoonsalt
1cup(227g)butter, at room temperature
1 ⅔cups(353g)granulated sugar
3largeeggs, at room temperature
1tablespoonvanilla extract
¾cup(170g)sour cream
Instructions
Preheat the oven to 350 degrees F. Line 2 standard cupcake pans with paper liners. In a glass liquid measuring cup, combine the cocoa powder and hot water and whisk until smooth.
In a medium bowl whisk together the flour, baking soda, baking powder, and salt.
In a medium saucepan over medium heat, combine the butter and sugar (I often do this in the microwave so I can use the same bowl for mixing). Cook, stirring occasionally, until the mixture is smooth and the butter is completely melted.
Transfer the mixture to the bowl of an electric mixer (or to a stand-alone bowl, using a handheld electric mixer) and beat on medium-low speed until the mixture is cool, about 4-5 minutes.
Add the eggs one at a time, mixing well after each addition and scraping down the sides of the bowl as needed. Blend in the vanilla and then the cocoa mixture until smooth. With the mixer on low speed, add the flour mixture in three additions alternating with the sour cream, beginning and ending with the dry ingredients and mixing each addition just until incorporated. So basically you'll add 1/3 of the flour, mix, then add 1/2 of the sour cream, mix, add another 1/3 of the flour, mix, add the rest of the sour cream, and finish with the last 1/3 of the dry ingredients.
Divide the batter evenly between the prepared liners, filling no more than 2/3 full. If you live at a high altitude or have had overflowing cupcakes in the past, err on the side of filling the liner of one cupcake 1/2 full and baking it alone first to judge how the cupcake will rise in the oven.
Bake the cupcakes until a toothpick inserted in the center comes out clean, about 15-18 minutes. Remove the cupcakes to a wire rack to cool completely.
Notes
Update:I feel a little silly I haven't tried this before now (5/2016) since this recipe has been on my site a while - if you were familiar with the original recipe it had some wacky measurements (1/2 cup plus 1 tablespoon cocoa powder, 1/2 cup plus 1 tablespoon water and 2 sticks plus 1 tablespoon butter). I made them today (for the millionth time) and decided to just nix all those extra tablespoons. And guess what? They turned out amazing. So I've edited the recipe but if you still feel strongly about those extra tablespoons, use the info in the parentheses above).