Preheat your oven to 180ºC.
Crush the digestive biscuits, either in a food processor or a mortar and pestle. Mix with with the butter and then push into a lined and greased cake tin (about 15cm/6 inches in diameter), to form the base of the cheesecake. Pop into the oven for 10 minutes, remove and allow to cool.
Meanwhile, beat the cream cheese, mascarpone, caster sugar and cornflour until well mixed and the sugar has dissolved (it helps if the ingredients are at room temperature). Add the egg, and vanilla extract and beat the mixture well until smooth. Finally, add the zest of the lime and mix through.
By now, your biscuit base should be cool enough to pour the cheesecake mixture over the top. Spread evenly over the biscuit base and try to smooth the top as much as possible. Cover with foil and bake in the oven at 180ºC for approximately 45 minutes. Removing the foil and baking for a further 10 minutes, taking care not to over brown. Remove the cheesecake from the oven and allow to cool.
To make the topping:
Combine all the ingredients in a pan, bring to the boil and simmer for about 20 minutes, or until the mixture has the consistency of a light jam.
Allow to cool, before pouring over the cheesecake.
Once the cheesecake has cooled completely at room temperature, refrigerate for 3 hours before serving!