Rinse the sticky rice under cold water until the water runs clear. Then soak the rice in water for at least 1 hour or up to overnight in the refrigerator to get a good texture.

Drain the soaked rice and place it in a heatproof bowl or steamer basket lined with a clean cloth. Steam the rice over boiling water for 20-25 minutes until the grains turn tender and slightly translucent.

While the rice steams, combine the coconut milk, granulated sugar, and salt in a small saucepan. Heat over medium heat, stirring until the sugar completely dissolves; do not let it boil. If you prefer a thicker sauce, stir in the cornstarch slurry and heat until slightly thickened.

Mix about 2/3 of the sauce into the steamed rice and let it rest for 5-10 minutes so it absorbs the flavors.

Serve by plating sticky rice with sliced mango and drizzling coconut sauce on top. Garnish with toasted sesame seeds if desired.