BASE

1. Grease an 8 inch springform cake tin.
2. In the work bowl of a food processor, pulse the biscuits until they are fine crumbs. Add the lemon and lime zest and melted butter, and pulse until combined. Press into the bottom of the tin, and refrigerate while you are making the topping.

FILLING

1. In a small pot over low heat, combine the lemon juice, lime juice and gelatine. Stir until the gelatine has dissolved. Set aside to cool slightly.
2. In the bowl of a stand mixer fitted with the whisk attachment, or using an electric mixer, whip the cream until soft peaks form. Transfer into a bowl. There is no need to wash the mixer between the cream and cream cheese mix. Whip the cream cheese and sugar in the mixer until smooth. Beat in the lemon and lime zest. Add the cooled juice and gelatine, and mix until well combined. Remove the bowl from the mixer, and using a spatula, gently fold in the cream. 
3. Spread the filling over the prepared base. Refrigerate for 4-6 hours until set, or overnight. Remove from the fridge about 45 minutes before serving. Run a small offset spatula or knife around the outside of the tin. Unclip the springform and remove carefully. Decorate with additional zest if desired.