Combine flour, sugar, and salt in top of double boiler. Add water and egg yolks,
mixing thoroughly.
Place over hot water and cook 10 minutes, stirring constantly. Be sure and cook
the full 10 minutes, even though it's getting thick, and keep stirring.
Remove from heat; add lemon juice and rind. Cool.
Pour into baked pie shell. Beat egg whites until foamy throughout. Add sugar, 2
tablespoons at a time, beating after each addition until sugar is blended. When
all sugar is added, continue beating until mixture stands in peaks. Pile lightly
on filling. Bake in moderate oven (350°F.) 15 minutes, or until meringue is
lightly browned.