Preheat the grill to medium. Spread out the hazelnuts on a baking tray and toast for 5 minutes under the grill. Leave to cool. Melt the chocolate over a pan of simmering water, leave to cool. Ground the hazelnuts in a food processor. Whisk the cream until stiff, then fold in the hazelnuts and reserve. Beat the egg yolks with 3 tablespoons of sugar for 10 minutes until thick. Whisk the egg whites in a clean, grease free bowl until soft peaks form. Whisk in the remaining sugar, a little at a time. Stir the cooled chocolate into the egg yolk mixture, then fold in the cream followed by the egg whites. Share the mixture between 6 freezer proof moulds, cover with cling film and freeze for at least 8 hours. Transfer to the refrigerator 10 minutes before serving. Turn out the Choconut Parfait onto serving plates and dust lightly with cocoa powder to decorate.