For the sponge:
175g butter or marg
175g caster sugar/any sugar I could find
3 eggs
3tbsp golden syrup (leftover from the snickers flapjacks)
175g self raising flour
a few tbsp of hot chocolate powder: the more, the better, and the less flour you'll need
Heat: 180c/ gas 4
Beat the butter & sugar, then add in the eggs and beat. Stir in the golden syrup. Sift over and fold in the flour, followed by several tablespoons of hot chocolate powder. The consistency should be runny enough for it to drop off the spoon: if not, add some water. Bake for 35 mins till the sponge is springy to the touch, or a knife comes out clean.
Icing:
Vanilla half: icing sugar + water + a drop of vanilla essence, with hundreds and thousands sprinkled over.
Chocolate fudge half: Hot chocolate powder + margerine +icing sugar, with chcolate sprinkles on top.
This would definitely pass the test of the hedonic calculus: many were made happy...