Tiered Chocolate Buttercream Cake Recipe | Ina Garten | Food Network

Ingredients

• 3 1/2 cups all-purpose flour
• 2 cups good cocoa powder
• 1 tablespoon baking soda
• 1/2 teaspoon kosher salt
• 1 1/2 cups (3 sticks) unsalted butter, at room temperature
• 1 1/3 cups granulated sugar
• 1 1/3 cups light brown sugar, packed
• 4 extra-large eggs, at room temperature
• 4 teaspoons pure vanilla extract
• 2 cups buttermilk, at room temperature
• 1 cup sour cream, at room temperature
• 1/4 cup brewed coffee
• Chocolate Buttercream Frosting, recipe follows
• 1 pound bittersweet chocolate
• 12 ounces semisweet chocolate
• 3/4 cup egg whites (4 to 5 extra-large eggs), at room temperature
• 1 1/2 cups granulated sugar
• 1/4 teaspoon cream of tartar
• 3/4 teaspoon kosher salt
• 1 1/2 pounds unsalted butter, at room temperature
• 3 teaspoons pure vanilla extract
• 3 teaspoons instant espresso powder, dissolved in 1 1/2 teaspoons water
• 3 tablespoons dark rum, optional