Marbled chocolate and vanilla cheesecake

Directions

• Set the oven to Gas Mark 3 (160°C / 325°F).
• Put the biscuits in a sturdy plastic bag and crush with a rolling pin.
• Mix the crushed biscuits with 2tbs sugar and melted butter. Press into the base of the tin to form an even layer. Set aside.
• Melt the chocolate over a pan of boiling water. When the chocolate has almost fully melted, add 125g sugar and incorporate it into the chocolate mixture and set aside to cool.
• In a large mixing bowl beat the cream cheese with the eggs, 150g sugar, sour cream and vanilla extract until well mixed with plenty of air bubbles on the surface.
• Pour half of the mixture into a separate bowl and set aside.
• Add the melted chocolate to the remaining cheesecake mixture and blend until smooth. Add the sultanas (if using) and mix them in.
• Pour in alternate amounts of the chocolate and vanilla mixture into the baking tin. Create swirls with a spoon.
• Bake for 50 minutes until golden brown. You may need to add 5 to 10 minutes extra to get the right colour.
• Leave to cool down completely before taking it out from the tin. The cheesecake will be at its best one or two days after baking.