Mix the biscuits and butter together, and press into the base of a springform tin.Sprinkle the gelatin over the water; allow to become spongy.
Dissolve by placing over boiling water or in the microwave oven (for 30 seconds on medium).
Combine the egg yolks, milk and sugar in a pan; place on medium heat and cook, stirring until slightly thickened.
Pour in the dissolved gelatin and lemon rind; set aside to cool slightly.Beat the lemon juice and vanilla into the cheese, then gradually stir in the gelatin mixture.
Fold in the stiffly beaten egg whites and three quarters of the whipped cream.Pour this mixture over the pie
crust.Refrigerate for several hours until firmly set.
Remove from springform and decorate with the remaining cream.