Put the hazelnuts in a dishtowel and crush them with the bottom of a pan. Put them in an ovenproof dish and bake them at 170 degrees in the oven.
Take them out when they turn golden and leave them to cool. Whip butter and sugar with a hand mixer until it becomes white and fluffy. Add the eggs one by one to avoid the dough from separating. Fold in flour, crushed hazelnuts, crushed chocolate and lime zest. Put the dough in a butter Lurpak® coated spring cake form and bake at 170 degrees for 25 minutes. Leave to cool.
Open the vanilla pod and scrape the marrow out onto a cutting board. Sprinkle over some sugar and crush the vanilla seeds with the flat side of a knife. Whip cream and sour cream together until it becomes stiff. Add the vanilla and powdered sugar. Arrange the cream on your cake and decorate with fresh berries.