A firm un-melty choc fudge icing?

[Blu]

help! It's warming up to be a boiling hot day, I have pledged a choc cake for the school fete...is there a sort of fudge icing which is like buttercream but has real chocolate in it so that it sets a bit firmer?

I have put the cake in the freezer, as I thought that would help it keep cool throughout the afternoon.

you could make a ganache - that's double cream and plain chocolate mixed together. Heat the double cream, take off the hob and then melt the chocolate in it. Put in fridge but keep an eye on it, you don't want it to set too much before you ice the cake.
Use 1 small pot of cream and a big bar of chocolate (150g maybe) and it should end up quite solid but not too hard.

Thanks, geekgrrl, I had imagined ganache to be quite sloppy - but I guess with a high choc to cream ratio, and using dark choc, it will be quite stiff.
Also will chill it in the fridge before taking it.
I'm the type who puts 'fate' in fete' - more domestic disaster then domestic goddess!