Rinse the rice under cold water until the water runs clear. Submerge the rice-filled sieve in cold water and soak for at least 1 hour, preferably 3 hours or overnight.

Drain the soaking water. In a pot, bring fresh water to a boil, and place the sieve with the rice over the pot, ensuring it doesn't touch the water. Cover and steam for 30-50 minutes until tender.

In a pan, combine 1 cup of coconut milk, ¼ cup of sweetener, and ⅓ teaspoon of sea salt. Bring to a boil, stir to dissolve the sweetener, then add the steamed rice. Cover and set aside for 45-60 minutes.

In a small pan, mix ½ cup of coconut milk, 1 ½ tablespoon of sweetener, a pinch of sea salt, and cornstarch. Bring to a boil and simmer for 1 minute until thickened.

On each plate, place ⅓ cup of warm coconut sticky rice, arrange mango slices beside the rice, pour thickened sauce over the rice, and garnish with sesame seeds or coconut flakes.