Bring the milk to a boil with the sugar, salt and vanilla. If you prefer lemon, shave a wide long ribbon of zest from the lemon in order to retrieve it easily. Rinse the rice and pour into the milk. Simmer very gently, using a heat diffuser if necessary. Cook until the rice is the same level as the milk. As it cools, the rice will absorb all the milk. Discard the lemon zest. This marvellous rice pudding can be served cold or warm. Accompany it with preserves, compotes, fruits in syrup or dried fruits.