Fill the mould completely with chocolate. Lay down a guitar sheet and smooth the surface. If you want the puzzle to remain whole without the pieces coming apart, press only around the edge, giving a slight extra thickness of chocolate in the center.
Turn the mould over (printed surface up). As soon as the chocolate begins to set, put in a cold place at 4°C/ 39,2°F for about 45 minutes.
Leave for another 15 minutes at room temperature (so that the chocolate is less brittle), then place the food carton under the puzzle and remove the excess chocolate from the sides and the mould. Slide all in the bag.
