Chocolate Stout Layer Cake with Chocolate Frosting

INGREDIENTS

• 3 ounces unsweetened chocolate, chopped
• 3 large eggs, separated
• 1/2 teaspoon salt
• 14 tablespoons (1 3/4 sticks) salted butter, room temperature
• 3/4 cup chocolate stout, regular stout, or porter
• 2 teaspoons baking powder
• 1 pound bittersweet chocolate (54% to 60% cacao), chopped
• 1 teaspoon instant espresso powder
• 1/2 teaspoon baking soda
• 2 cups heavy whipping cream
• 1 1/4 cups plus 3 tablespoons sugar
• 2/3 cup freshly brewed strong coffee
• 2 1/4 cups all purpose flour