melt 4oz margarine, 2tbsp sugar and 1tbsp golden sugar in a pan before mixing in 3tbsp cocoa powder
crush 6oz biscuits (digestives are good) either in a food processor or with a rolling pin in a bag
add the chopped marshmallows, prunes and cherries (if using) to the biscuits and then pour on the melted mixture and stir well
pour the mixture into a tray lined with clingfilm. using a flat spatula flatten the mix firmly into the tray
melt 200g chocolate in a pan and then spread evenly on the top of the tiffin
put in the fridge for 3 hours to solidify and then cut into squares. keep in fridge.