Combine 3 tablespoons corn startch with 1 cup plus 2 tablespoons sugar in top of double boiler. Add the grated rind of one lemon, 4 tablespoons lemon juice, 1 tablespoon butter and 3 egg yolks, beaten.
Mix well then add 1 1/2 cups boiling water very slowly. Cook over hot water until very thick. Cool. Pour into pastry shell. Beat 3 egg whites until almost stiff, then add 6 tablespoons sugar while continuing to beat stiff. Arrange meringue on filling. Bake 30 minutes at 300 degrees.