Line 13x9-inch pan with foil, with ends of foil extending over sides. Mix wafer crumbs and butter until blended. Press onto bottom of prepared pan. Bake 10 min.
Separate 1 egg and refrigerate yolk until ready to use. Beat cream cheese, 1 cup sugar, flour, lemon zest, 2 tbsp of lemon juice and vanilla in large bowl with mixer until blended.
Add egg white and remaining 3 whole eggs, 1 at a time, mixing on low speed after each just until blended. Pour over crust.
Bake 40 min. or until center is almost set. Cool 1 hour. Refrigerate 4 hours.
Mix cornstarch and remaining sugar in medium saucepan, gradually stir in water and remaining lemon juice until blended. Bring just to boil on medium heat, stirring constantly. Cook and stir until clear and thickened.
Lightly beat reserved egg yolk in small bowl with fork until blended. Stir in 2 tbsp of the hot cornstarch mixture.
Return to remaining cornstarch mixture in saucepan. Stir until blended. Cook 1 min. or until thickened, stirring constantly. Cool slightly.