Rinse the rice until the water runs clear, then soak it in cold water for at least one hour.
Drain the rice and steam it in a bamboo steamer or a regular steamer basket for 20 to 25 minutes until tender.
While the rice cooks, heat the coconut milk, sugar, and salt in a small saucepan over medium heat until the sugar dissolves. Do not let it boil.
Transfer the cooked rice to a bowl and pour half of the warm coconut mixture over it. Stir well and let it sit for 15 minutes to absorb.
Serve the sticky rice with fresh mango slices, drizzle with the remaining coconut sauce, and sprinkle with sesame seeds.