1. Line the tin with baking parchement. Place the biscuits in a freezer bag and crush to fine crumbs with a rolling pin.
2. Melt the butter in the microwave for one minute.
3. Stir the crumbs inot the butter until well mixed, then firmly press the mix into the base of the tin.
4. Soak the gelatine in the lemon juice for 5 minutes.
5. Melt it in a bowl set over a pan of simmering water.
6. Remove from the heat and cool for 3-5 minutes.
7. With an electric whisk, beat together the cream cheese, caster sugar and lemon zest until very smooth, making sure there are no lumps.
8. Clean the whisk attachments, then whisk the double cream in a bowl until it forms soft peaks.
9. Whisk the gelatine into the cream cheese mixture until well mixed, then carefully fold the double cream into this mix.
10. Fold the whipped cream in very gently, making sure you don't lose any volume.
11. Spoon the filling into the prepared cake tin, smoothing the surface so it is flat and even.
12. Chill for at least 3 hours or overnight until firm.
13. Transfer in to a serving plate from the cake pan and enjoy!