Place the chocolate in a thin-sided bowl and suspend over a gently simmering bain-marie, ensuring that the bowl does not touch the water. Melt the chocolate and allow to cool a little.
Finely crush the biscuits in a plastic bag using a rolling pin or blitz them in a food processor, mix with the butter and half of the chocolate. Spread the mixture over the bottom of the prepared cake tin and press down firmly with the base of a glass.
Cream cheese mixture
Using the whisk on a hand mixer, combine the cream cheese, sugar, eggs and cornflour. Stir in the chocolate chunks and remaining melted chocolate and spread over the biscuit base.
For approx. 40 mins. in the centre of an oven preheated to 180°C. Remove from the oven, allow to cool slightly, remove the tin frame, slide the cheesecake onto a cooling rack and leave to cool. Top with the chocolate.