Combine sugar, flour, and salt in top of double boiler; add egg, water, and lemon juice, mixing thoroughly. Place over boiling water and cook 10 minutes, stirring constantly. Add lemon rind and butter. Cool. Makes about 1 1/3 cups filling, or enough filling for two 8x8-inch layers, or three 9-inch layers. Kate Smith Collection 1940 Published by General Foods Corp.