To decorate you will need:
Pashmak Persian fairy floss (can be bought from Harvey Nichols), or regular fairground candy floss (from Ocado), yellow and pink ombré, chocolate disks (see below) and indoor sparklers.
To make the Ombre Chocolate Disks:
You will need a 24-hole silicone mini muffin tin. First you need to temper your white chocolate. Working very quickly, add touches of colour to the mix. Fill a few moulds about 0.5cm thick with this paler chocolate, then gradually add more colouring to the bowl of chocolate and fill a few more moulds to build up the ombré effect. Leave to set at room temperature, then pop the chocolates out of the bases.
To make the lemon and raspberry sponges:
Preheat the oven to 180°C/gas 6 and line the base of two 18cm cake tins with baking paper, greasing the sides with butter.
Beat the butter and sugar in a large bowl until pale and fluffy. Add the eggs one at a time, scraping the sides of the bowl to make sure everything is well mixed. Sift in the flour, then fold in the milk, lemon zest and raspberries. Be careful not to over-mix the batter – you want to keep it as light, fluffy and airy as possible.
Divide the mixture evenly between the prepared cake tins and smooth over with a palette knife. Bake in the oven for 30–40 minutes, until golden-brown and springy, then leave to cool for about 15 minutes before turning out on to a wire rack to cool completely.
To make the buttercream:
Using a hand-held whisk, electric whisk or stand mixer, whip the butter and icing sugar together until they are light and fluffy, adding milk to loosen. You want your buttercream to be spreadable but firm.
Divide the buttercream between two bowls. To one bowl, add the lemon curd and yellow colouring to give a lovely lemony pastel yellow shade. To the other bowl add a handful of squished raspberries and pink colouring to give a bright pink. Don’t mix completely – that way it has a nice marbled effect.
To assemble:
Layer the sponges using your lemon and raspberry buttercream alternately, plus any extra lemon curd.
To ice, use a palette knife to spread thick smears of pink and yellow icing randomly all over the outside of the cake. Make sure you clean your palette knife in between scooping the buttercream. Decorate with fairy floss in the centre and surround with pink and yellow ombré chocolate disks.
Dim the lights and bring out the sparklers!