1    Basic sponge cake
Mix/recipe
Red food colouring
Yellow food colouring
Blue food colouring
Green food colouring
Black food colouring
Whipped cream
500 g  Bar of cadburys bournville
Or similar slab of dark
Chocolate

Right. Bring all your ingredients together as you would for a normal
cake until you get to the stage where youd normally stick it in the
oven. Now, divide the cake into 5 equal amounts with each amount in a
separate bowl with some form of stirring apparatus (wooden spoon
would be ideal) Into four of the five pour about 3 Tbls. of food
colouring (but not the black, 1 colour in each) and stir in really
quickly. It might curdle a bit here but if you stir it enough it
should be ok (either that or add the colour a little at a time) when
you have your 4 coloured segments put them to one side. Now break off
about 4 chunks of the chocolate. Eat them. Better? Good. Melt the
rest of the chocolate and when its good and runny stir it in to the
final 5th of the cake mix. Now taking dollops from each colour at a
time (you should have green, red, blue, yellow and brown) splat them
into a cake tin trying not to get any 1 dollop touching another
dollop of the same colour. Sling this into your oven/furnace or
whatever and leave it to cook for however long your sponge recipe
suggests.

In the meantime make up some standard icing (or frosting as they say
in the American parts of the world) and whang in loads of the black
food colouring until you get a really dark grey (you might need to
thicken up the icing a bit here as it tends to go over runny).
Finally add a small amount of red and a small amount of blue food
colouring to the whipped cream and give it a good stir so it all goes
purple.

Now wait for the cake to finish cooking….

….is it done? well dont look if it isnt or itll sink….

…finished? good. Turn out the cake (which should look like a
patchwork with any luck) onto a rack and leave to cool for a bit.
When its cool enough saw it in half horizontally and slap the cream
in the middle (the colours inside should be incredibly vivid compared
to the outside). Reassemble the 2 halves and throw on the icing.
Leave to set. You should now have an absolute frankenstein of a cake
with metallic looking icing that is incredibly chocolatey due to the
incredibly chocolatey brown bits!