Place the butter in a saucepan and melt over a low heat. Place the biscuits in a food processor and blitz until crushed. Add the cocoa powder and then, with the mixer on a low speed, slowly pour in the melted butter. Once combined, pour the mixture into your cake tin and press down firmly to create the cheesecake base. Chill in the fridge while you prepare the rest of the recipe.
Preheat the oven to 140'C.
Break the chocolate pieces into pieces and place in a heatproof bowl. Bring the cream to the boil, pour it overt the chocolate and then stir continually until the chocolate has melted and the mixture is smooth and glossy.
Zest the orange and then place the zest in a bowl with the cream cheese, sugar, egg yolk and the cornflower. Beat until smooth and then fold in the chocolate mixture. Spoon the cheesecake mix on to the base and flatten the surface with the back of a spoon.
Transfer to the oven and bake for 30 minutes. Remove from the oven, allow to cool and then chill in the fridge overnight for best results.
«The cheesecake is cooked when it is well cooked around the edges but retains a slight wobble in the centre. Allow to cool in the tin.»