Start by making the rice - rinse the rice with cold water until the water runs clear.
Add the rice and a cup and a half of water to a pan set over a low to medium heat.
Place a lid on the pan and cook it until all the water is evaporated and the rice is cooked.
Take the pan off the heat, but keep the lid on for a further 5 minutes.
In a separate pan, add the coconut milk and sugar and bring it to a boil over a medium heat.
Pour the hot sugary coconut milk over the cooked rice, and stir well.
Set aside for 30 minutes for the rice to soak up the liquid.
To make the coconut sauce, add the coconut milk and sugar to a pan set over a medium heat.
Bring it to a boil, then make a slurry from the cornflour and water, and add it to the pan.
Stir until the sauce thickens slightly.
Divide the rice between ramekins or small round bowls pressing down well. with a spoon, then place a small plate over the bowl and turn it over, so that the rice can have the shape of a dome.
Sprinkle some of the seeds over each rice dome, drizzle some of the coconut milk and serve with mango slices.