Rinse and soak the rice under cold running water until the water appears clear. Soak in enough water to cover for a minimum of 2 hours, or ideally overnight.
Drain the rice and prepare your steaming apparatus. Steam the rice over boiling water for approximately 30-35 minutes until fully cooked and translucent.
While the rice steams, heat coconut milk in a medium saucepan with granulated sugar and sea salt over medium heat, stirring until the sugar dissolves without boiling.
Transfer the cooked rice to a large mixing bowl, pour 1 cup of warm coconut milk mixture over it, and gently fold to combine. Let it rest for 15-20 minutes.
On a serving plate, add a scoop of sticky rice in the center, arrange sliced mangoes on top, and drizzle with remaining coconut milk mixture.
Sprinkle toasted sesame seeds over the dish and garnish with fresh mint leaves if desired.