1. Put the rice, coconut milk, salt and sugar in a saucepan with 300 ml / 1/2 pint water. Stir them and bring to the boil. Stir again and simmer, uncovered, until all the liquid has been absorbed by the rice, about 8-10 minutes. Remove from the heat, cover the pan and leave it to stand for 5 minutes.
2. Transfer the rice to a steamer or double saucepan, and steam for 15-20 minutes.
3. To serve : arrange on the serving plate, with the mangoes pieces.