Rinse the glutinous rice under cold water until the water runs clear.
Soak the rice in water for at least 4 hours or overnight.
Drain the soaked rice and steam it in a bamboo or metal steamer for about 20-25 minutes.
While the rice is steaming, combine coconut milk, sugar, and salt in a saucepan over medium heat.
Stir until the sugar dissolves, then remove from heat.
Once the rice is cooked, transfer it to a bowl and pour half of the coconut sauce over it.
Mix well, cover, and let it sit for about 15 minutes to absorb the flavors.
Peel and slice the mangoes into thin pieces.
To serve, place a portion of the sticky rice on a plate and arrange the mango slices beside it.
Drizzle the remaining coconut sauce over the top and sprinkle with sesame seeds.