Method Prep:15min › Extra time:12hr chilling › Ready in:12hr15min
Blitz the biscuits until no chunks are left. In a bowl mix the melted margarine with the crumbs. Press into a greased and lined 20cm baking tin and leave to chill for 15 minutes. If the biscuit mix doesn't look evenly coated in margarine melt some more and pour over. Check to make sure there are no dry patches on edges, as this can cause the entire base to crumble when removing from tin or cutting to serve.
Whisk the cream, condensed milk and cream cheese until thick. Add the lemon zest (reserve some for the decoration) and juice and mix well.
Spread over cake and leave to chill for 1 to 2 hours, ideally over night as the topping really sets and the flavour improves.
Decorate topping with lime zest and grated chocolate.