Chocolate Stout Cake

INGREDIENTS

• 1 tablespoon baking soda
• 4 large eggs
• 1 1/2 cups unsweetened cocoa powder (preferably Dutch-process)
• 2 cups (4 sticks) unsalted butter
• 2 cups stout (such as Guinness)
• 4 cups sugar
• 1 1/2 teaspoons salt
• 2 cups whipping cream
• 1 1/3 cups sour cream
• 4 cups all purpose flour
• 1 pound bittersweet (not unsweetened) or semisweet chocolate, chopped