Preheat your oven to 170C/150C fan, and line two 8"/20cm deep cake tins with parchment paper.
Add the butter and sugar to a bowl, and beat till light and fluffy.
Add in the flour, cocoa powder and eggs and beat again until a lovely smooth cake mixture is formed.
Split evenly between the two tins and bake in the oven for 50-60 minutes (or until a skewer comes out clean!)
Once baked, leave to cool in the tin for 10 minutes, and then leave to cool fully on a wire rack.
Chocolate Buttercream
Beat the unsalted butter on its own for a while in your mixer until its smooth and supple.
Add in your icing sugar and cocoa powder a little at a time and beat fully until its light and fluffy!
(If the mixture is really stiff, add in 1-2tbsp of boiling water and beat fully to smooth out)
For the Ganache
Add the the dark chocolate orange and milk chocolate orange to a large bowl.
Add the cream to a pan and heat till just before boiling point. Pour over chocolate and leave to sit for 5 minutes. Once sat, mix until smooth (Add back to the pan if its not quite melted).
Leave the ganache in a bowl and stir every few minutes until it forms a peanut butter like consistency - you can do this in the fridge as well, just make sure to stir it so it doesn't set too quickly!
Whip the ganache with an electric whisk until it is fluffy, light and mousse like!
Assembly.
Level the cakes off if necessary. Split the two cakes into two so you have four layers in total.
Add your first cake to a cake board (I use a large 10" cake board) and secure with a small amount of buttercream.
Spread some chocolate buttercream onto the first layer, add the second sponge. Repeat until you reach the top layer of cake.
Spread some chocolate buttercream around the sides to fill in the gaps and create a crumb coat. Refrigerate the cake for at least 30 minutes.
Once refrigerated and the ganache is ready, using an angled spatula, slather over the chocolate ganache and then smooth around using a large metal scraper.
Carefully press some sprinkles into the bottom of the cake (like shown in the photos)!
Once the sprinkles are on the cake, refrigerate the cake for another 30 minutes.
Drip
Melt the white chocolate until smooth. Carefully drip down the sides of the cake, and fill in the top of the cake with the chocolate!
Decoration
Pipe some swirls of the leftover buttercream on top using a medium 2D closed Star Piping Tip and decorate with the sprinkles and chocolate orange segments on top!
Notes
You can swap the chocolate orange chocolates for a plain dark chocolate and a plain milk chocolate - I just love chocolate orange!
You cannot swap the dark for just milk though - please use what is written in the recipe!