Ingredients:

For the cake:

• 1¾ cups all-purpose flour
• 2 cups sugar
• ¾ cups high-quality cocoa powder such as Valrhona
• 2 teaspoons baking soda
• 1 teaspoon baking powder
• 1 teaspoon kosher salt
• 1 cup whey instead of buttermilk
• ½ cup vegetable oil
• 2 eggs + 1 extra yolk at room temperature
• 1 teaspoon pure vanilla extract
• 1 cup freshly brewed hot coffee

For the Chocolate Buttercream Frosting:

• 6 ounces semisweet chocolate preferably Valrhona
• ½ pound 2 sticks unsalted butter, at room temperature
• 1 extra-large egg yolk at room temperature
• 1 teaspoon pure vanilla extract
• 1¼ cups sifted confectioners' sugar
• 1 tablespoon instant coffee granules such as Nescafé