Before starting, place your mixing bowl in the fridge overnight (or at least one hour) for your frosting.
Preheat your oven to 350°F/175°C. Butter or grease two 8 inch baking pans and line it with parchment paper.
Combine the flour, cocoa powder, sugar, baking powder, baking soda, and salt in the bowl of a stand mixer, using the paddle attachment. Set aside
In a large jug, combine the buttermilk, oil, eggs, and vanilla extract.
While the mixer is on low speed, slowly pour in the ingredients from the large jug
While the mixer is still running, slowly add the hot water and mix. Your batter will be very thin. Make sure the mixer is on your lowest speed so it doesn't splash everywhere
Pour the batter into the prepared pans. Bake for 35-40 minutes, until a toothpick comes out clean when inserted
Allow the cakes to cool for 10 minutes before removing from the pans. Let them cool completely on a cooling rack.
Make Frosting
In your chilled mixing bowl in the stand mixer fitted with the whisk attachment, beat your heavy cream, salt, sugar and vanilla extract on low speed for 2 minutes. The sugar should dissolve by then.
Turn the speed to high for 2-3 minutes until thick and resembles Greek yogurt.
With the mixer on your lowest speed, add the cream cheese a tablespoon at a time. Once it is all added, stop the mixer and scrape the bottom and sides of the bowl. Start the mixer again and beat on high speed for 3 minutes until thick. Add in the cocoa powder and beat again for 1 minute.
Assembly
Place one cooled cake layer down and top with half of the frosting. Place the other cake layer on top, and top that with the remaining frosting. Use an offset spatula to cover the sides of the cake with frosting, then use a large spoon to create swoops and swirl. Add sprinkles or chocolate shavings to the top.
Notes
My recipes have been developed and tested in cups and metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way.I make sure that all of my ingredients are at room temperature before I start the recipe, so pull out all of the ingredients before you start baking.Salt: If you don’t have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt.Buttermilk: If you don’t have buttermilk, replace it with an equal amount of sour cream or full fat yoghurt. You can also make your own buttermilk, for every cup of buttermilk add 1 tablespoon of lemon juice to 1 cup of milk and let sit for 5 minutes. Vegetable Oil: Use an unflavoured oil like rapeseed or canola oil if you don’t have vegetable oil. Storage: Keep tightly wrapped in the fridge for up to 5 days. Let it come to room temperature before eating.
Making Ahead: You can make the cake layers ahead of time. Bake them and then once completely cooled, wrap in plastic wrap tightly. Store in the fridge for up to 2 days or in the freezer for up to 2 months. If frozen, allow to defrost and come to room temperature before frosting the cake.