Place crackers in a bag and crush fine with a rolling pin.
Combine with 1/4 cup sugar and softened butter and mix well.
Put crumbs in a refrigerator ice cube tray.
Press firmly against bottom and sides of tray with a cup.
Soften gelatine in cold water.
Combine slightly beaten egg yolk, milk and 1/2 cup sugar; cook over low heat for 5 minutes, stirring constantly.
Remove from heat; add gelatine and stir until dissolved.
Blend cheeses together; a'dd lemon rind and vanilla.
Add gelatine mixture and blend well.
Chill until mixture begins to thicken.
Beat cream until foamy; add lemon juice and whip until thickened.
Beat egg white until stiff.
Fold cream and egg white into cheese mixture.
Pour into crumb lined refrigerator tray.
Chill until firm.
Cut into pie shaped wedges for serving.