Irish Chocolate Stout Cake

Ingredients

• 1 cup Irish stout beer (such as Guinness®)
• 1 cup butter, cut into pieces
• 3/4 cup unsweetened cocoa powder
• 2 eggs
• 2/3 cup sour cream
• 2 cups all-purpose flour
• 2 cups white sugar
• 1 1/2 teaspoons baking soda
• 3/4 teaspoon salt
• 3 cups confectioners' sugar, or as needed
• 1/2 cup butter at room temperature
• 3 tablespoons Irish cream liqueur (such as Baileys®), or as needed
• 8 ounces bittersweet chocolate, coarsely chopped
• 2/3 cup heavy cream
• 2 tablespoons butter at room temperature