Thanks for the quick reply ... geez there's alot of Aussies on this forum! 
No, I melted the copha first. The recipe said to "melt copha over gentle heat. Remove from heat and stir in cocoa powder and vanilla."
I then tried to melt some sugar in the copha (which had melted) but it wouldn't dissolve. I was thinking it would be like dissolving sugar in melted butter ... but no go.
I  didn't have any icing sugar left, so I ended up melting some dark chocolate with the copha, as that's all I had.
It's in the fridge now, so I haven't tried it yet. But no doubt it will be too bitter for my like!
There must be a way of sweetening cocoa powder so it mixes with copha, surely??? I didn't want to drive 20 mins to the shop to get some milk chocolate cooking chocolate, but next shop I will get some. It was more a case of "why the blazes won't the sugar dissolve.
Thanks again!

Yes, I thought of that too. But I didn't want the 'soft' butter icing with the slice, as opposed to the crisp icing with the copha - another question whilst we're on the subject ...
I took it out of the fridge and tried to cut it, well, talk about difficult! The chocolate crust layer just split all over the show and came away from the peppermint underneath. It actually doesn't taste too bad, though not good enough to do again from that particular recipe. I find that's the problem with 'internet' recipes ... some are really good, some not so. Very much trial and error. That was another reason I registered with this site, as Jamie's recipes are generally good, and I would imagine the people on the site have good recipes too.
Yes, I agree regarding the  reference to the chocolate in the recipe. I think they meant drinking chocolate too.
Thanks yet again for your input.

I discovered the crackly chocolate the first time I tried to use it as an icing on caramel slice.  It's a tricky judgment call.  Chocolate in a block can be pretty hard to cut or break.  No recipe ever really says this, but I find when using it as an icing, it has to be set just to a certain point and no more, so that it's still soft enough to slice through with a sharp knife, but not so soft that the knife will just drag rather than cut it.  I always tend to err a bit on one side or the other ...

But if the chocolate is a bit too hard set, cutting it with a hot knife can help; just have a cup or bowl of boiled water, dip the knife in till the knife is hot, then quickly wipe dry with a teatowel and cut away.  When the knife cools down, repeat the process until the slice is all cut.

Yes, Mummza, Copha is a vegetable oil shortening product predominantly made from coconut oil.  It's seriously good artery-clogging stuff that's been used in Australia for decades.  It's best known as a primary ingredient in Chocolate Crackles, where you make a mixture of Rice Bubbles (the breakfast cereal), icing sugar, dessicated coconut, cocoa and melted Copha; then you blob the mixture into patty cake papers and refrigerate it.  First-rate fete fare.

White Christmas is a similar thing, made from Rice Bubbles, milk powder, icing sugar, dried fruit and Copha.

Hi Mummza. Copha is different because it is hydrogenised coconut oil (which makes it unhealthier I understand). It is so very Australian although they have it under different names elsewhere.