Beatty's Chocolate Cake

INGREDIENTS

• 1 1/4 cups sifted confectioners' sugar
• 1 cup buttermilk, shaken
• 1 tablespoon instant coffee powder
• 1/2 pound (2 sticks) unsalted butter, at room temperature
• 1 teaspoon kosher salt
• 2 cups sugar
• 2 teaspoons baking soda
• 1/2 cup vegetable oil
• 1 extra-large egg yolk, at room temperature
• 2 extra-large eggs, at room temperature
• 1 cup freshly brewed hot coffee
• Chocolate Buttercream, recipe follows
• 6 ounces good semisweet chocolate (recommended: Callebaut)
• 1 3/4 cups all-purpose flour, plus more for pans
• 1 teaspoon pure vanilla extract
• 1 teaspoon baking powder
• Butter, for greasing the pans
• 3/4 cups good cocoa powder