Rinse the Rice: Place the rice in a fine mesh strainer (sieve) and rinse in cold water until the water runs out clear. (This removes some of the stickiness.)
Soak the Rice: Soak the rice in warm water for 60 minutes, or up to several hours. Pour the rice back into the sieve.
Steam the Rice: Place large pot over medium heat. Add 2 inches of water and place the sieve with the rice over the water. Cover the pot with a lid and bring to a boil. Steam the rice for 30 minutes. Toss the rice in the sieve to flip it over, so the top of the sticky rice is now at the bottom of the sieve. Cover and continue steaming another 10-20 minutes until fully cooked.
Mix the Sauce: Meanwhile, in a small sauce pot, mix the coconut milk, sugar, and salt. Set over medium heat and warm until the sugar has fully dissolved into the coconut milk. Set aside.
Rest the Rice: Mix the cooked sticky rice into the sauce. Cover and let the rice pudding rest for 30 minutes. Then peel and dice (or slice) the mangoes.
To Serve: Scoop the rice pudding into a 4 ounce ramekin. Press firmly to pack the rice together. Then flip the ramekin over onto a dessert plate and wiggle to release the rice from the ramekin. Repeat making 8 portions total. Scoop the diced mango over top of each pile of sticky rice. Sprinkle with sesame seeds if desired. Serve cold or a room temperature.
The texture should be sticky and a little saucy, but not wet.Cooled leftovers can be sealed in an airtight container and stored in the refrigerator for up to a week. The flavors will be even better a day or so after the coconut sticky rice is made! But do note that the consistency of the rice will continue to thicken and get stickier once the dish is chilled and sits in the fridge.Enjoy the leftover mango sticky rice cold straight from the fridge, or reheat in 30 second bursts in the microwave until desired temperature is reached.