Mix cereal and butter. Press 3/4 c firmly on bottom and sides of an 8″ pie pan. Blend egg yolks and 1/4 c sugar in top of double boiler. Mix in salt, lemon rind and lemon juice. Cook and stir over boiling water until slightly thickened, about 5 min. Cool. Whip cream just until soft peaks will form and fold in lemon mix. Beat egg whites until foamy throughout. Add 1/4 c sugar gradually and continue beating until stiff peaks will form. Fold in cream mix and pour into crust. Sprinkle with remaining cereal mix. Freeze until firm, about 4 hours.