I've got one in the freezer - At least I think it was supposed to be a mars bar, looks a bit funny but tastes really nice.
I mixed a chocolate sachet to a thick consistency, placed on greaseproof paper, then mixed vanilla to a slightly more runny consistency and spread over the top of the chocolate, wrap paper around and place in freezer - I left tonight's one about an hour but it could have done with an extra 10 - 15 mins.
This makes two, one for today, one for tomorrow.