Step 1: Preheat the Oven

Preheat your oven to 350°F (175°C). Grease two 9-inch round cake pans and line the bottoms with parchment paper.

Step 2: Prepare the Dry Ingredients

In a large mixing bowl, sift together the flour, sugar, cocoa powder, baking powder, baking soda, salt, and espresso powder (if using). Whisk to combine evenly.

Step 3: Combine the Wet Ingredients

In another bowl, whisk together the buttermilk, vegetable oil, eggs, and vanilla extract until smooth.

Step 4: Mix the Batter

Gradually add the wet ingredients to the dry ingredients, stirring until just combined. Slowly pour in the boiling water, mixing gently. The batter will be thin—this is normal and ensures a moist cake.

Step 5: Bake the Cakes

Divide the batter evenly between the prepared pans. Bake for 30–35 minutes, or until a toothpick inserted into the center comes out clean. Allow the cakes to cool in the pans for 10 minutes, then transfer them to a wire rack to cool completely.

Step 6: Make the Ganache Frosting

1. Heat the heavy cream in a small saucepan over medium heat until it just begins to simmer.
2. Remove from heat and pour over the chopped chocolate in a heatproof bowl. Let sit for 2 minutes.
3. Stir until smooth and glossy. Add the butter and vanilla extract, mixing until fully incorporated. Let the ganache cool to room temperature before frosting.

Step 7: Assemble the Cake

1. Level the cake layers if necessary. Place one cake layer on a serving plate or cake stand.
2. Spread a generous layer of ganache frosting on top.
3. Add the second cake layer and frost the top and sides of the cake with the remaining ganache.

Step 8: Decorate and Serve

Decorate with chocolate shavings, sprinkles, or berries, if desired. Slice and serve immediately or refrigerate until ready to enjoy.