Store Cupboard Chocolate Orange Cake appears in How to be a Domestic Goddess and widely online. Basically you melt butter and chocolate, then stir in a jar of marmalade, eggs and sugar, then fold in flour and bake. I decorated mine with grated orange zest and a nasturtium, which is edible.
And it was very popular with my colleagues at the coffee morning, raising money for Macmillan, which was the whole point.