To begin with, take a cup of raw sticky rice in a container and rinse it properly. Use your hand to gently stir the grains. It is important to do so for some time and then drain the water to remove the excess starch. Repeat this process one more time and then add water to soak the rice. You need to soak this rice for at least 1 hour or 5 hours, depending on your preference. Once done, rinse again and drain the water, 

After you are done with this process, place this rice in a heatproof bowl, and add water to your steamer or electric pressure cooker, and not into the rice, Place the rice-filled heat-proof bowl on the steaming rack in the steamer or inside the cooker filled with 2-inches of water. Turn to medium-high heat to allow the water to boil. When the steam begins to come out of the pot, reduce it to medium heat. Allow the rice to steam this way for 20-25 minutes until it is thoroughly cooked, with no raw grains. Once done, remove the pot and keep it aside and begin to prepare the coconut sauce.

Take a saucepan, and add coconut milk, sugar, and salt. Stir in the ingredients properly. Now, cook over medium heat so that the sugar is properly dissolved and the mixture properly combined. Ensure that it does not boil but sufficiently heats up. 

Meanwhile, take a small bowl and mix cornstarch with 4 tablespoons of water, Stir well so that the cornstarch dissolves. Add this mixture to the coconut milk, sugar, salt-mix that's being heated and keep stirring it till it thickens. You can adjust the thickness as per your preference by adding more cornstarch and water. Ensure that the sauce doesn't become too thick in the process as that just doesn't go well with the dessert, 

Once the sauce is prepared in your desired consistency, add half of it in the bowl containing the sticky rice. Mix the two very well. Allow the rice and sauce mixture to cool before serving. Remember the sauce will begin to thicken once it begins to cool, so add more sauce to dilute it. 

Transfer the rice, once cooled, in serving bowls or plates. Cut the ripe mangoes into slices and place them next to the rice on the plates. Pour in some more coconut sauce over it. Sprinkle some toasted sesame seeds or caramelized, golden-brown mung beans over it as a garnish and you are good to go! Enjoy the delicious dessert!