• 2 cups stout (such as Guinness) I used Overcast espresso stout from Oakshire Brewring in Eugene, Oregon. 
• 2 cups (4 sticks) unsalted butter
• 1 1/2 cups unsweetened cocoa powder (preferably Dutch-process)

• 4 cups all purpose flour
• 4 cups sugar
• 1 tablespoon baking soda
• 1 1/2 teaspoons salt
• 4 large eggs
• 1 1/3 cups sour cream

Icing

• 2 cups whipping cream
• 1 pound bittersweet (not unsweetened) or semisweet chocolate, chopped

Cake: Preheat oven to 350 degrees. Butter three 8″ round cake pans with 2″ sides. Line with parchment paper. As mentioned, I used two pans. 

Bring 2 cups stout and 2 cups butter to simmer in heavy large saucepan over medium heat. Add cocoa powder and whisk until mixture is smooth. Cool slightly.

Whisk flour, sugar, baking soda, and 1 1/2 teaspoons salt in large bowl to blend. This seemed like a ton of flour and sugar to me, but it worked!

Using electric mixer, beat eggs and sour cream in another large bowl to blend. Add stout-chocolate mixture to egg mixture and beat just to combine.

Add flour mixture and beat briefly on slow speed. Using rubber spatula, fold batter until completely combined. Divide batter equally among prepared pans.

Bake cakes until tester inserted into center of cakes comes out clean, about 35 minutes. (Because I made just two layers they may have been thicker.  I had to bake my cakes for about 40 – 45 minutes. I used the extra batter to make a baby cake in a loaf pan.) Transfer cakes to rack; cool 10 minutes. Turn cakes out onto rack and cool completely.

Icing:
Bring cream to simmer in heavy medium saucepan. Remove from heat. Add chopped chocolate and whisk until melted and smooth. Refrigerate until icing is spreadable, stirring frequently, about 2 hours. It took about 3 hours to get the icing to a proper, spreadable consistency. If it gets too thick, just warm slightly over a bain marie.  

I inverted the cakes again after cooling and sliced the tops off with a serrated knife to  flatten.

Place 1 cake layer on plate. Spread 2/3 cup icing over. Top with second cake layer. Spread 2/3 cup icing over. Top with third cake layer. Spread remaining icing over top and sides of cake. (Adjust for layers.)