1 tablespoon plain gelatin
1/4 cup water
4 eggs, separated
1 cup sugar
1/2 teas. salt
1 1/2 teas. grated lemon rind
6 tablespoons lemon juice
Soften gelatin in 2 tablespoons water.  Combine slightly beaten egg yolks, 1/2 cup sugar, salt, lemon rind and juice and remaining 2 tablespoons water; cook over boiling water until mixture thickens, stirring constantly.  Add softened gelatin, stirring until gelatin is dissolved; cool until mixture begins to thicken.  Then gradually beat remaining 1/2 cup sugar into stiffly beaten egg whites and fold into lemon-gelatin mixture.  Turn into baked pastry shell and chill until firm.  When ready to serve, top with whipped cream.
This comes from the Home Institute Cook Book that Aunt Edith sent to me for Christmas the year I was in St. Louis.