Melt chocolate and butter on a water bath (Bain-Marie). When almost melted, stir in instant coffee, cocoa powder, salt, nutmeg, muesli and corn syrup. You can also add raisins or nuts to the mixture. Turn of the heat and let it cool. After a while, add puffed rice to the mixture and stir everything well, so every grain will be coated with chocolate. Spread the mixture into a thick layer on an aluminum foil. Make sure its well compressed to the bar would not crumble. Freeze it for an hour, cut or brake into pieces and keep in s sealed container in the freezer.