Preheat the oven to 170°C/325°F/Gas mark 3.

To make the crumb case, crush the biscuits/cookies to fine crumbs in a food processor or place in a clean, plastic bag and bash with a rolling pin. Transfer the crumbs to a mixing bowl and stir in the melted butter. Press the buttery crumbs into the base & sides of the prepared cake pan firmly using the back of a spoon. You need the crumbs to come up about 3-4cm/1½ inches high on the side of the pan so that they make a case for the filling. Wrap the outside of the pan in cling film/plastic wrap and place in a roasting pan half full with water, ensuring that the water is not so high as to spill out. Set aside.

For the filling, whisk together the cream cheese, crème fraîche, eggs, sugar, melted chocolate, finely chopped ginger, syrup and chopped chocolate in a large mixing bowl. Sift the flour over the mixture and stir in, then pour the mixture into the crumb case. Bake in the preheated oven for 1-1¼ hours until set but still with a slight wobble in the centre. Turn off the heat and leave to cool completely in the oven, then transfer to the refrigerator to chill for at least 3 hours or preferably overnight.

Once chilled, melt the white and dark chocolate for the decoration in separate, heatproof bowls set over 2 pans of simmering water. Leave to cool slightly, then spread the white chocolate in a thin layer over the top of the cheesecake. Spoon the dark chocolate into the piping bag and pipe swirls over the top of the cheesecake in pretty patterns. If you don't have a piping bag, you can swirl patterns of the chocolate using a spoon. Chill in the refrigerator until the chocolate has set before serving.