Start by mixing the crushed biscuits and butter together and press into the bottom of the cake tin. Place in the fridge to chill while you make the filling. In a large bowl, mix together the cheeses and sugar till smooth, then mix in the eggs till well incorporated. Place 2/3 of the mixture into another bowl, adding in the cocoa powder and melted chocolate. Mix together till you have a smooth chocolate cheesecake filling. Add the vanilla essence or vanilla pod seeds to the remaining 1/3 of the cheesecake mixture and mix well. Spoon the chocolate and the vanilla cheesecake filling alternatively onto the chilled biscuit base, using a skewer to mix the 2 colours together to produce a marbling effect. Bake the cheesecake in the oven at 170c, for about 1 hour on the middle shelf. The cheesecake should be firm to touch when it is cooked. Remove the vanilla and chocolate marbled cheesecake from the oven and leave to cool completely before removing from the tin. To serve the cheesecake, sprinkle the top with cocoa powder. Suggested accompanying wine: DELICATA Casella Moscato sweet white wine