You can try to extend the shelf life of a jar of Nutella. The jar will have a 'best before' date which the manufacturer has calculated from the data of thousands of experiments, so it's asking a lot to want to find a way of simply storing Nutella, which the manufacturer would have missed. That said, store unopened Nutella in a dark, cool place, keeping it well away from sunlight and heat. One thing, though. Once you open the jar, the clock starts ticking, and all bets are off. You've only got a week or two before the stuff goes wonky and loses its zing.