Grate carefully the rind of the lemon and squeeze out the juice, add juice to sugar in saucepan and stir a moment. Beat the yolks of eggs until light and creamy, beat the whites until stiff. Put juice and sugar over fire and boil a moment, add the grated rind and pour gradually over the yolks, beating constantly. Return to the fire a minute. Remove and beat in by spoonfuls the stiffly beaten whites. Give all a good beating and pour at once into a baked crust, which should be hot. Bake a nice brown and serve hot or cold.