Heat the oven to 140°C. Use wax paper to line a 20cm springform cake tin.
Making the crust: Process the biscuits in a food processor until they look like fine crumbs.
In a bowl, combine the melted butter with the biscuits. Transfer into the cake tin and even out, pressing down to form a crust. Put in the oven for about 10 minutes.
Remove from the oven and leave to cool down.
Making the topping: Meanwhile, melt the chocolate in a bain-marie. Leave aside to cool.
Whisk the rest of the topping ingredients with 2 tablespoons of cold water until smooth (about 1 or 2 minutes). Divide the mixture into 2 separate bowls. Add the melted chocolate to one of the bowl and stir well.
Alternate spoonfuls of the plain mixture with spoonfuls of the chocolate mixture onto the biscuit crust. Using a palette knife, make some swirls through the topping to get the marble effect.
Lay the tin onto a baking tray then put in the oven for about 50 minutes, until set yet soft. Turn off the heat, open the door and let the cheesecake cool down in the oven.
Remove from the oven and put in the fridge for at least 1 hour.
Sprinkle with white and dark chocolate flakes and serve.