Start this recipe by preparing the praline. Place the sugar and 2 tbsp water in a clean pan and cook to a caramel until golden in colour. Quickly add in the hazelnuts, cover in the caramel and pour over an oiled sheet of baking paper. Spread out and allow to cool down completely. When ready, chop 1/3 into pieces. Next , place the mascarpone, cream, icing sugar and vanilla pod seeds into a bowl whisk together for a minute till smooth. Mix in ½ of the hazelnut liqueur and the 1/3 of chopped praline. Line a loaf tin with baking paper and spread out 1/3 of the cream mixture. Dip the savoiardi biscuits in the cold espresso mixed with the remaining hazelnut liqueur and lay on top of the cream. Repeat this process again 2 more times. Cover with cling film and freeze for at least 6 hours. When ready to serve, remove the semifreddo from the paper and place onto a serving plate. Decorate the top with the remaining 2/3 caramelized hazelnuts and lightly dust with cocoa powder and serve immediately.