For the base: Melt the butter in a saucepan, then remove from the heat. Place the biscuits in a food processor and blitz until fine crumbs. Add the crumbs to the melted butter and stir to combine.
Tip the crumb mixture into a greased and lined 28-centimeter tin (11-inch springform pan) and press down firmly with the back of a spoon.
For the filling: Put the cream cheese in a bowl and beat until soft and creamy. This will prevent lumps from forming and make it easier to combine with the other ingredients. Add the condensed milk and beat again until well-combined and smooth. Stir through the lime juice and rind, reserving some of the rind to decorate.
Whip the cream to soft peaks, then fold it through the cream cheese and condensed milk mixture. Pour over the base and smooth over with the back of a spoon. Place in the fridge and leave to set, at least 12 hours or preferably overnight.
When set, remove from the tin and transfer to a serving plate or cake stand. Sprinkle over the remaining zest just before serving.