Beatty's Chocolate Cake

Ingredients

• all-purpose flour
• sugar
• good cocoa powder
• teaspoons baking soda
• teaspoon baking powder
• teaspoon kosher salt
• buttermilk, shaken
• vegetable oil
• extra-large eggs, at room temperature
• teaspoon pure vanilla extract
• freshly brewed hot coffee
• Chocolate Buttercream Frosting, recipe follows
• ounces good semisweet chocolate, such as Valrhona
• pound unsalted butter, at room temperature
• extra-large egg yolk, at room temperature
• sifted confectioners' sugar
• tablespoon instant coffee powder