Start the recipe by melting the butter in a saucepan. Add the crushed biscuits and chopped hazelnuts and mix well. Press the mixture into the base of an 18cm spring-bottom cake tin lined with greaseproof paper, and bake in the oven for 10 minutes at 200`c. Meanwhile prepare the cheesecake filling by putting the mascarpone, ricotta, eggs, sugar and vanilla essence in a large bowl. Using an electric beater, mix the ingredients together to a smooth consistency. Add the melted chocolate and continue mixing till well incorporated. Finally, fold in the raisins and whole hazelnuts, and pour the cheesecake filling on top of the prepared biscuit base. Even the mixture out using a palette knife and bake in the middle shelf of your oven for 1 hour and 15 minutes at 150`c. When the cooking time is up, turn off the oven, and leave the cheesecake inside it has cooled completely. Take the cheesecake from the oven and carefully remove it from the cake tin and onto a large round serving plate. Finally, decorate the top of the chocolate cheesecake with chocolate curls and serve.