This cake is very, very easy! Just throw everything into a food processor and whizz until mixed. You can mix it by hand if you really want to, but it's much faster my way ;)
Pour the mixture into a large square pan and bake at 180C/350F/Gas Mark 4 for about 20 to 30 minutes (until a sharp knife comes out clean). Leave it to cool in the tin for a few minutes before turning it out onto a wire rack to cool completely.
To decorate mine I cut a little bit off the top and bottom to make it more flag shaped, and then covered it in about 150g of melted milk chocolate. Once cooled I used some white chocolate frosting to add the skull and crossbones (alright, so I stole Mike and asked him nicely to draw them for me! ;))
To make the white chocolate frosting melt together 90g white chocolate, 40ml of double cream, 40g butter and then mix in 60g of icing sugar. Although, that actually made about 3 times as much frosting as I needed! So you might want to halve the recipe, or draw something which requires more icing :)