Grease and then line two 18cm tins with baking parchment.
Beat 250g of the butter with the brown sugar and 100g of the caster sugar until creamy and pale.
Gradually beat in the eggs, then mix in the Vanilla Extract.
Mix the flour, Baking Powder, cinnamon and ginger then sieve into the bowl with the butter mixture, gently fold together.
When almost combined add the milk and continue to fold until smooth. Divide between the tins, smoothing the tops, bake for 25mins or until an inserted skewer comes out clean.
For the buttercream; beat the remaining butter and icing sugar until smooth and creamy.
Add the lime zest, juice and cream cheese, gently whip until combined (don’t overmix or it may become runny).
Put the remaining caster sugar in a small saucepan with 100ml of water, mix then put on a low heat to dissolve. Bring to the boil, then allow to bubble for 1 min (it should be just over 100C).
Take off the heat, squeeze the excess water from the Gelatine then stir into the sugar mixture, and then mix in the cream until smooth. Pour this over the White Chocolate then blend or carefully mix until very smooth.
Strain through a sieve then divide between five bowls – making one with just over a third of the mixture and the rest even.
Dye the larger portion with a few drops of the Black Food Gel; the others with varying amounts of the Blue or Purple Gels to make light and dark shades (though not too dark so they show against the black). Set aside to cool and firm up, stirring now and again (if it goes too solid just pop in the microwave for a few secs).
Meanwhile, spread the jam over the top of one of the sponges, with a palette knife, spread a layer of buttercream then press the other sponge on top. Palette the remaining buttercream around the sides and top of the cake ensuring it is smooth. Set aside on a wire rack placed over a tray.
Once the glaze is thick enough to pour, pour the black into the bowl with the darker blue or purple.
Then dispense this over the cake and drizzle over the other colours, concentrating mostly on one side. Use a spatula to cover any bare patches.
Gently swirl the colours together with the palette knife.