Prepare the Sticky Rice:

1. Rinse the glutinous rice under cold water until the water runs clear.
2. Soak the rice in water for at least 4 hours or overnight.
3. Drain the rice and steam it in a bamboo steamer or a regular steamer for 20-25 minutes, or until the rice is tender and translucent.

Make the Coconut Sauce for the Rice:

1. In a saucepan, combine 1 cup coconut milk, sugar, and salt. Heat over medium heat until the sugar dissolves. Do not boil.
2. Once the rice is cooked, transfer it to a bowl and pour the warm coconut mixture over it. Stir gently to combine. Let it sit for 15-20 minutes to absorb the flavors.

Prepare the Coconut Topping Sauce:

1. In a separate saucepan, combine ½ cup coconut milk, sugar, and salt. Heat until the sugar dissolves and the mixture thickens slightly. Set aside.

Assemble the Dish:

1. Slice the mangoes and set aside.
2. Place a portion of the sticky rice on a plate, add mango slices alongside, and drizzle the coconut topping sauce over the rice.
3. Garnish with toasted sesame seeds or mung beans if desired.