1 1/2 cups (12 fluid ounces) stout or dark beer (I used Guinness)
1 1/2 cups (340 grams/12 ounces/3 sticks) unsalted butter, cut into cubes
1 cup sifted (115 grams/4 ounces) King Arthur Double-Dutch Dark Cocoa or Dutch-process cocoa (I use Cacao Barry Cocoa Powder – Extra Dark)
3 cups (360 grams/12.5 ounces) all-purpose flour
3 cups (600 grams/20.5 ounces) granulated sugar
2 1/4 teaspoons (12 grams/11.25 mL) baking powder
1 teaspoon (8 grams) salt
3 large eggs, at room temperature
2/3 cup ( 165 mL) sour cream, at room temperature
1. Preheat oven to 350°F. Grease two 9-inch round pans (2″ deep), line bottoms with parchment paper circles, then grease circles, dust with flour and tap out excess. Set aside.
2. Place the stout and butter in a large, heavy saucepan and heat on medium heat until the butter melts, stirring occasionally. Remove the pan from the heat, and whisk in the sifted cocoa powder until smooth. Pour into a large heatproof measuring cup or bowl and let cool.
3. In a medium bowl, whisk together dry ingredients: flour, sugar, baking powder and salt. Set aside.
4. In the bowl of an electric mixer fitted with the paddle attachment (flat beater), mix the eggs and sour cream on medium speed (I use #4 on KitchenAid) until well combined, about 3 minutes.
5. Add the cooled cocoa mixture, and mix on medium speed (I use #4 on KitchenAid) until combined, about 1 minute.
6. Add the dry ingredients slowly and combine on low-speed (I use #2 on KitchenAid) until blended, making sure to scrape the sides and bottom of bowl, and then mix for another minute.
7. Divide batter into prepared pans evenly. If possible, weigh the pans and batter with a kitchen scale for accuracy and even layers. If you do, each pan of batter should weigh ~1 kg/2.2 lbs. Place cake pans on middle oven rack side-by-side, but about 2″ apart and bake until toothpick inserted into centre comes clean, about 35 minutes.
8. Let cakes cool on wire racks for ~10 minutes, loosen edges with knife or small palette knife, then gently remove from pans to cool completely.