Beat the unsalted butter on its own for a while in your mixer until its smooth and supple and starting to whiten.
Add in your icing sugar a little at a time and beat fully until its light and fluffy and add the vanilla extract!
(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.
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 the rest of the white buttercream around the cake and then smooth around using a large metal scraper.
Once the buttercream is smooth, prep your sprinkle area. I create a barrier with objects like boxes of foil and clingfilm around my turntable.
Get a bowl with all of your sprinkles in.
Using the palm of your hand, grab large handfuls of sprinkles and gently push the sprinkles up the sides of the cake without pressing too hard to move the cake.
The movement is like your are wiping the sides of the cake with the palms of your hand - but the sprinkles will push in as you go. The excess will naturally fall off.
Keep repeating until the cake is covered - I cover the top too.
In a small bowl or jug, add the milk chocolate, dark chocolate and double cream and melt carefully in short bursts in the microwave, stirring well each time, until smooth.
Carefully pipe this onto the cake to create a drip - Set the cake in the fridge for another 30 minutes.
You can use any sponge you want as a base - my chocolate fudge cake sponges are fudge and delicious, my chocolate drip cake has a delicious basic chocolate sponge, or you can jazz it up with more flavours - or even a rainbow cake!