Separate the eggs and beat the whites until soft peaks form, beat in 3 tablespoons of the sugar and continue beating the whites until glossy.
In the top half of a double boiler; beat the egg yolks until thick. Beat in 1 cup of the sugar, the flour, and salt. Mix thoroughly. Add the boiling water slowly, stirring constantly. Stir in the vinegar.
Cook egg yolk mixture over hot water until mixture is thick and smooth. Stir in the salt and the lemon juice. Pour the batter into one 9 inch baked pie shell. Cover top of pie with meringue.
Bake at 325 degrees (165 degrees C) for 20 minutes. Allow to cool before serving.