In a bowl, mix the coconut milk with the sugar and salt. Set aside.
To steam the rice
Soak the rice in water overnight. Rinse and drain.
To steam the rice, layer the washed rice on a cheesecloth and fold it. Place on a steamer, and steam for 20 minutes.
When the rice is steamed, place it in a bowl. And pour the rice soak over it, mix well. Set aside, and let it soak up the sauce for 20-30 minutes.
To make the coconut sauce
In a small saucepan, combine the coconut milk with the sugar and water and let it reach a simmer (do not boil). Make the slurry by combining the cornstarch with water, and whisk it in the coconut milk. Cook for a couple of minutes until the sauce slightly thickens.
Peel and slice the mango into thick slices. Serve the rice in a plate or a bowl, arrange the mango slices on the side, and drizzle with sauce. Sprinkle with sesame seeds.
This dessert only works using glutinous or sticky rice that you can find at most Asian stores.
Garnish with toasted sesame seeds, and/or nigella seeds.
Serve over a banana leaf if you can find it.
It is strongly recommended that you consume the sticky rice on the same day after it was cooked, as storing it in the fridge will harden it and make it a bit gummy.