1.Combine biscuit crumbs and butter in a medium bowl. Press mixture firmly over base and side of a 23cm pie plate; refrigerate 30 minutes or until firm.
2.To make filling, stir egg yolks, 1/3 cup of the caster sugar, gelatine, rind, juice and the water in medium heatproof bowl over medium saucepan of simmering water until mixture has thickened slightly. Remove from heat; pour into a large bowl. Cover and cool to room temperature. Mixture should be set to about the consistency of unbeaten egg white before remaining ingredients are added.
3.Beat egg whites in small bowl with electric mixer until soft peaks form. Add remaining sugar gradually, beating until dissolved after additions. In two batches, fold egg white mixture through lemon mixture.
4.Spread filling into crumb crust. Refrigerate several hours or until set.