Melt
the remaining butter in a pan. Chop the chocolate into pieces and add
to the melted butter. Melt slowly over a low heat.
Spread
the chocolate on top of the mars mixture and leave to cool. Cut the crispie
cake into squares and enjoy.
You can eat these still warm or straight from the fridge. If you eat them
chilled make sure they are thin otherwise they can be a bit difficult
to eat.