While steaming, prepare the sauce for the rice. Add the 1/2 cup of coconut milk to a sauce pan along with the 1/3 cup sugar & 1/2 teaspoon salt, and stir over low heat until dissolved. Set aside.
Prepare the topping sauce as well. In another small sauce pan, add the 1/2 cup coconut milk, 1/4 teaspoon salt, and 1 teaspoon rice flour / tapioca starch. stir over low heat until thickened, and remove from heat.
When the rice is finished, Remove to a bowl and add the sauce(the sauce you made first)Dont add it all leave a little bit so the sticky rice will not wet. Then cover with tin foil or lid. Let the rice absorb the coconut milk for 15-20 minutes. If your sticky rice is wet put it in microwave for 5-10 min.
Peel the mango , cut in half then cut in to pieces on both side . Spoon an equal amount of sticky rice next to it, and top with a few spoons of the thickened sauce. Garnish with toasted mung beans or sesame seeds