Preheat the oven to 180°C.
Mix the flour, sugar, vanilla seeds, and hazelnuts in a bowl.
Beat the eggs and butter until fluffy and combine with the flour mixture to form a dough ball.
Turn the dough onto a floured surface and roll into two 24cm long rectangles with 1cm thickness.
Bake on a baking sheet for 20 minutes until golden.
Cool for 15 minutes, cut into 12 biscuits per sheet using a cutter, and bake for 15 more minutes until crisp.
Dust the cooled biscuits with icing sugar.
Soak gelatine leaves in cold water for 15 minutes.
Macerate half of the raspberries with icing sugar and liqueur.
Heat the remaining raspberries with caster sugar until dissolved, then stir in the softened gelatine.
Purée the mixture until smooth and let it cool.
Fold the lemon zest and whipped cream into the raspberry purée.
Layer the macerated raspberries and mousse into glasses and garnish with biscotti.