• Preheat oven to 350°F. Line three 8-inch round cake pans with parchment paper and spray with baking spray.
  baking spray
• In a large bowl, whisk together flour, cocoa powder, sugar, baking powder, baking soda, and salt.
  2 cups all-purpose flour, ¾ cup unsweetened Dutch-process cocoa powder, 1 ½ teaspoon baking powder, ½ teaspoon baking soda, ¾ teaspoon salt, 2 cups granulated sugar
• Stir in vegetable oil until dry ingredients are well coated, followed by eggs and vanilla.
  ¾ cup vegetable oil, 2 large eggs, 2 teaspoon pure vanilla extract
• Stir in buttermilk until combined, then carefully pour in hot coffee and stir until smooth.
  1 cup full-fat buttermilk, 1 cup hot brewed coffee
• Add batter evenly to prepared cake pans and bake in preheated oven for 20 minutes, or until a toothpick entered into the center of the cakes comes out smooth or with moist crumbs.
• Cool cake layers slightly in cake pans, then transfer to a wire rack to cool completely before adding frosting.

Chocolate Mousse Filling

• Heat 1 cup of your heavy cream in microwave until hot, but not boiling, about 1-1½ minutes.
  2 ½ cups heavy cream
• Pour hot cream into chopped chocolate; stir to melt. Add another cup of chilled heavy cream, vanilla and salt. Chill overnight.
  8 oz bittersweet chocolate, 1 teaspoon pure vanilla extract, pinch salt, 2 ½ cups heavy cream
• When ready to assemble cake, use a hand mixer to whip cooled ganache just until stiff peaks form – do not overmix. It should only take about 30 seconds.
• In a separate bowl, whip remaining ½ cup of heavy cream with powdered sugar until stiff peaks form. Fold into gently into whipped ganache mixture.
  2 ½ cups heavy cream, 1 tablespoon powdered sugar
• Spread mousse evenly over cake layers -- I use about 1½ cups of mousse filling between each layer, and use the rest for the top and sides.
• Chill assembled cake in fridge for at least one hour to allow mousse to set.
• If adding ganache, heavy cream in microwave until hot, but not boiling, about 1-1½ minutes.
  1 cup heavy cream
• Pour over chopped chocolate and mix to melt until smooth. Stir in vanilla and salt.
  8 oz bittersweet chocolate, ½ teaspoon pure vanilla extract, pinch salt
• Allow ganache to cool to room temperature or chill in fridge for up to one hour so that it's no longer warm to the touch.
• Spread cooled ganache over chilled cake and allow to set. Store cake in refrigerator and serve chilled.