There are different recipes of langoustines. To cook griddled langoustines with hazelnut butter, thread the langoustines cautiously onto the skewers and chill for up to a day. For the butter, thinly grate or chop half the hazelnuts, then chop the rest. Then, when ready to serve, melt the hazelnut butter in the pan, heat a griddle pan or barbecues, then brush the langoustines with the oil. Griddle each skewer for one to two minutes, turning, until pink and just cooked. Pile on a platter, pour half the hazelnut butter over the langoustines, and then serve the rest in a small bowl for dipping.