Preheat the oven to 180 C / Gas 4. Grease a 20cm springform cake tin.
Combine the crushed biscuits and melted butter and mix well. Press this mixture into the bottom of your greased cake tin, and place in the fridge to chill while you make the filling.
Put the mascarpone cheese, lime zest, lime juice, sugar and egg yolks in a bowl and whisk until thick and creamy. Then sprinkle in the cornflour and fold in.
In a separate clean bowl, whisk the egg whites with a pinch of salt, until stiff peaks form. Fold the fluffy egg whites into the cheese mixture (do this gently and slowly, this will help the finished cheesecake to be light and fluffy).
Spread the mixture on top of the biscuit base in the cake tin and smooth the top.
Bake in the oven for 35 minutes. It should be firm to the touch when it's ready. Allow to cool for 3 hours, and then chill in the fridge.