Method

• 1.
  Preheat the oven to 180°C. Grease a 23cm round springform pan. Place 2 layers of aluminium foil on the outside of the pan (this prevents water seeping into the pan while cooking in the water bath).

• 2.
  Crush the biscuits in a food processor. Combine melted butter with biscuit crumbs and press into the base of the pan.
• 3.
  Place the cream cheese, 170g caster sugar, eggs, egg yolks, 2 teaspoons vanilla extract and the lemon juice in a food processor. Process until smooth, then pour over the biscuit base. Place the cheesecake in a large roasting pan and pour boiling water into the roasting pan to come halfway up the sides of the springform pan. Bake in the oven for 1 hour.
• 4.
  Beat together sour cream, remaining sugar and vanilla and pour over the cake. Return to oven for a further 10 minutes. Remove from oven and set aside in the pan to cool, then refrigerate for 4 hours. Serve dusted with cocoa powder.