Store the bar in a cool, dry place away from direct sunlight, heaters or a warm car. Like most chocolate, it can soften when exposed to heat, and the filled centre may become less defined if the bar gets too warm. This does not necessarily mean the taste is spoiled, but the appearance, snap of the chocolate shell and contrast between creamy filling and crisp kataifi may change.
If the bar arrives or becomes slightly softened, let it rest in a cooler room before opening. Avoid repeatedly warming and chilling it, because temperature changes can affect the surface of chocolate and may reduce the pleasant texture of the filling. If you choose to chill it briefly before eating, give it a few minutes at room temperature so the milk chocolate and pistachio filling are not too hard and the flavour is easier to notice.
For travel or a work bag, keep it away from items that generate heat and do not leave it in direct sun. The 55 g size makes it easy to take with you, but it is still chocolate, so storage matters if you want the creamy filling and light crunch to stay close to the intended texture.