Preheat the oven to 350F/175C.

Line and grease three eight-inch cake pans, or four seven-inch pans.

Combine 2 cups all-purpose flour, 2 cups sugar, ¾ cup black cocoa powder, 2 tsp baking powder, 1 ½ tsp baking soda, and 1 tsp salt in a large bowl. Whisk together until combined.

Add 1 cup of hot water and 2 tsp instant espresso or coffee in a separate, medium-sized bowl. Stir until dissolved.

Add 1 cup buttermilk, ½ cup oil, 2 eggs, and 2 tsp vanilla extract to the instant espresso mixture. Give the mixture a quick stir to combine the ingredients.

Pour the wet ingredients into the dry ingredients and mix by hand until fully incorporated. The batter will be on the thin side, but that’s the consistency you're after!

Divide the batter evenly between the cake pans, and bake for about 25 minutes.

Remove the cake layers from the oven and let them cool in the pans for about 10 minutes.

Gently run an offset spatula around the rim of the cake pans to loosen them, then flip them into wire racks to finish cooling.

Once cooled, use a serrated knife to level the top of each cake layer.

Beat 2 cups of unsalted butter on a medium speed for 30 seconds with a paddle attachment until smooth.

Add 1 cup black cocoa powder, 1 tsp vanilla extract, and ½ tsp fine salt. Mix on low until the ingredients are fully incorporated.

Slowly mix in 5 cups of powdered sugar. Halfway through, add in ⅔ cup of heavy cream to make the frosting easier to mix.

Mix in 1 ⅓ cups of melted and cooled dark chocolate on a low speed. Mix until the ingredients are fully incorporated and the desired consistency is reached.

Stack and frost cake layers on a greaseproof cake board, using a dab of frosting to help stick the first cake layer to the board.

Add an even layer of buttercream between each cake layer with a large offset spatula.

Spread a thin coat of frosting around the cake, fully covering the cake layers. Smooth using a bench scraper, then chill the cake in the fridge (30 minutes) or freezer (10 minutes) until the frosting is firm to the touch.

Add a second, thicker layer of frosting to the cake and smooth using a bench scraper.

Decorate as desired and enjoy!