Preheat your oven to 170ºC/150ºC Fan, and line two 8"/20cm deep cake tins with parchment paper.
Add the butter and sugar to a bowl, and beat until 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.
Buttercream
Beat the unsalted butter on its own for a while in your mixer until its smooth and supple.
Add in your icing sugar a little at a time and beat fully until its light and fluffy and add the vanilla extract and food colouring!
(If the mixture is really stiff, add in 1-2tbsp of boiling water and beat fully to smooth out)
Decoration
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 or flat serving plate and secure with a small amount of buttercream.
Spread some buttercream onto the first layer, add the second sponge. Repeat until you reach the top layer of cake.
Spread some buttercream around the sides to fill in the gaps and create a crumb coat. Refrigerate the cake for at least 30 minutes.
Once refrigerated, using an angled spatula, spread a thin layer of buttercream around the middle section of the cake and carefully press in the sprinkles with the palm of your hand and then smooth around using a large metal scraper.
Chill the cake again for another 30 minutes.
Once chilled, pipe or spread some more buttercream in a thicker layer around the top section and bottom section of the cake and then smooth around using a large metal scraper. Smooth some buttercream on to the top of the cake as well.
Refrigerate the cake for another 30 minutes.
I then used some rose gold paint to paint around the edges of the fault line, and then also flicked some onto the other sections of the cake.