The traditional method using a steamer:
Soak the sticky rice in enough water to cover the rice for at least a hour (best if overnight). With your steamer, put water in the bottom and cover the steam section with cheese cloth. Pour the sticky rice on the cheesecloth, cover with the lid and put it on the stove on medium to high heat. The sticky rice should take about a 20 minutes of steaming to cook and will become translucent when done.
The Microwave Method:
Soak the sticky rice for 10 minutes in warm water in a bowl.[b] Soaking the rice is very important.[/b] The water level should be just above the rice, which comes out to be 1 cup of rice and a little over 1 cup of water (about 10% more). I recommend using a non-plastic container because you may melt the plastic in the microwave. Cover the bowl with a dish and cook in microwave for at full power 3 minutes. Stir the rice around to move the rice from the top to the bottom. You will notice that some of the rice is translucent or cooked and some still has white center or the uncooked portion.
Heat it up again for another 3 minutes. Check and see if it is done. When cooked, all the rice should be translucent. If it needs more cooking, I recommend heating up and checking every 3 minutes or so. How long it takes to cook really depends on your microwave.
Heat the coconut milk in a pot over medium heat. Stir constantly and let the coconut milk simmer. Hard boiled coconut milk will curdle.
Add sugar and salt.
Remove from heat. Pour 3/4 of the hot coconut milk over the hot sticky rice. Let it sit for 5 minutes. The sticky rice will absorb all the coconut milk. The rice should be a little mushy.
Spoon the rest of the coconut milk on top of the rice at serving time.
Peel and slice ripe mango. Place sticky rice on a small plate and top with mango.