Melt the chocolate by microwaving at 30 second intervals, stirring in between, till melted. But be careful not to scorch the chocolate! Otherwise, melt in a double boiler.
For a thicker base, you can make the tiffin in a smaller tin, like a 20cm square tin. If using a smaller tin, you can reduce the chocolate used to about 225g (8 oz).
This was amazing, but what made it even better was double the amount of golden syrup and 6tsp cocoa. I used Ginger nuts instead of rich tea/digestives and threw in some fresh chopped ginger (about a thumb sized piece) I only used dark chocolate on the top. Made it at 7pm lastnight, by 7:30 it had gone. Ooops. - 05 Jul 2012
Altered ingredient amounts. Didn't seem to have quite enough raisins in mine so I added a couple of extra handfuls - 14 Feb 2010
Delicious! I was a bit confused by the 'swiss roll tin' though. I used a small roasting dish which did the job fine. Very nice indeed! - 14 Feb 2010