i used to make this no-bake mars bar tray thing regularly:
3 mars bars, 3 and a half oz. of marg, 3 cups rice crispies.
melt mars bars and marg in pan, stir in crispies, spread in flat tin, fridg for an hour.
cream together l and a half oz. marg and 6 tablespoons of icing sugar, add some cocoa powder (doesn't say how much), spread over crispie mixture and fridge again.
it's just a bit of a more luxurious, grown up twist on crispie cakes and dead easy, especially being a fridge thing and not a baked one. always went down a treat.