1. Preheat the oven to 140C/120C fan/gas 1. Line the base of a 20cm non-stick, springform cake tin with greaseproof paper.

2. For the base: tip the digestive biscuits into a food processor and blend to fine crumbs (alternatively, tip them into a plastic bag, seal and bash with a rolling pin). Mix well with the melted butter then tip into the prepared tin and press down to form an even base. Bake for 10 minutes then set aside to cool.

3. For the topping: while the base is cooling, melt the chocolate in a heatproof bowl set over a pan of barely simmering water (make sure the bowl doesn't come into direct contact with the water or the heat will be too fierce). When melted, set aside to cool slightly.

4. Place all of the remaining filling ingredients into a large mixing bowl with 2 tablespoons of cold water and beat together for 1-2 minutes until smooth. Pour half of the mixture into a clean mixing bowl and stir in the melted chocolate.

5. Place alternate spoonfuls of white and dark topping onto the biscuit base then swirl a palette knife lightly through the topping to create a marble pattern.

6. Place the tin on a baking sheet and bake for 50 minutes, or until set but still with a slight wobble to the mixture (the cheesecake will set as it cools). Turn off the oven, open the door and leave the cheesecake in the oven until completely cool (this should stop cracks appearing on the top).

7. When completely cooled, transfer to the fridge to chill for at least 1 hour, or until ready to serve. Decorate with white and dark chocolate flakes, if using.