Melt the butter and sugar together in a saucepan over a gentle heat and then pour into a bowl containing the crushed biscuits. Mix thoroughly.
Line a 23cm springform cake tin with greaseproof paper. Spoon the biscuit mixture into the tin and press it down to form a firm, well-packed base. Leave in the fridge to set for about 30 minutes.
Meanwhile, make the filling. Beat the cream cheese in a bowl to soften it and then add half the sugar and the lemon zest. In a seperate bowl, mix the sour cream, double cream, the remaining sugar and the vanilla extract together and then whisk until it forms firm peaks - you should be able to turn the bowl over your head and the mixture be firm enough to stay put.
Fold the cream cheese mixture into the cream and then pour it all onto the chilled biscuit base. Chill for at least 4 hours or preferably overnight.
You can top with fruit. We used fresh strawberries mixed with a little bit of icing sugar to bring out their sweetness.
Recipe courtesy of Lisa Faulkner