Dead simple.
You get those ready to bake ones from the dairy cabinet. (You know, the ones in the can that you twist the paper off and roll out.)
Next add the measly little pieces of plain chocolate that the give you with it.
THEN........
Get some chocolate, say, some Dairy milk. Chop into similarily small pieces( but LOTs more ) and add to the rest. Roll it yp and bake off.
Then when ready, DON'T touch the butter dish. Instead get some chocolate spread and cover the top or bottom of the pastry with it. If you completely cover it you can't hold it and your friends/family will stare in disgust due to the fact that they think you are holding a turd.
Enjoy.