Line the base of a loose-bottomed 20cm cake tin. Crush the biscuits until they are a fine crumb. Mix the biscuit crumbs with the melted butter and cocoa powder until combined and then press into the base and evenly up the sides of the tin. Leave to chill for 30 minutes.
Soak five of the gelatine leaves in a small bowl of cold water and leave for 5 minutes until softened. While the gelatine soaks, combine the mascarpone and sour cream until smooth. Drain the water and squeeze the excess water from the gelatine. Transfer the gelatine to a small saucepan and heat over a low flame, stirring, for 2 minutes until melted. Remove from the heat and add the cheese and cream mixture along with the cinnamon. Beat until smooth and combined.
Using an electric hand whisk, beat the eggs and 100g of the sugar in a medium bowl for 4 minutes until pale and thick enough to leave ribbons on the surface. Fold into the cheese and cream mixture. Pour into the biscuit crust. Chill for 3-4 hours or until set.
Soak the remaining gelatine in cold water for 5 minutes. While the gelatine soaks, gently heat the mulled wine in a small saucepan over a low flame. Remove from the heat. Drain the water from the gelatine and squeeze out the excess water. Add to the warm wine along with the remaining sugar and stir until dissolved. Allow the mixture to cool. Once cold, carefully spoon over the cheesecake. Transfer to the fridge and chill for another 2-3 hours until completely set.
Spread the melted chocolate on the bottom of a large plate. Place in the fridge for 2 minutes until the chocolate is firm but not rock solid. Angling a small sharp knife away from you, scrap the chocolate to create curls. If they break, leave the chocolate at room temperature for 30 seconds. If it becomes too soft, leave it in the freezer for up to a minute. Pile the chocolate curls on the centre of the cheesecake to serve.