Rinse the sticky rice with tap water and use your hand to gently stir it. Drain the water to remove the excess starch. Repeat once, then add water to cover. Soak the sticky rice for a minimum of 1 hour, up to 5 hours. Rinse again and drain the water.

Transfer the rice to a heatproof bowl, add about 2 inches of water to your steamer (not into the rice), place the heatproof rice bowl on the steaming rack in the steamer, and cover the steamer. Turn to medium-high heat to bring the water to a boil. When the steam starts to come out of the pot, turn to medium heat. Steam for 20 to 25 minutes, until the rice is cooked through, with no hard raw bits in the middle. Remove the pot from the stove. Let sit, covered, while you prepare the sauce.

Add the coconut milk, sugar, and salt to a saucepan. Cook over medium heat until the mixture is hot and the sugar is melted. Do not bring the coconut sauce to a boil.

Combine the cornstarch and 4 tablespoons water in a small bowl. Stir to completely dissolve the cornstarch. Add half of the slurry to the sauce. Stir immediately to thicken the sauce. You can adjust the thickness of the sauce by slowly adding a bit more water or cornstarch slurry, if needed. The sauce shouldn’t be too thick, but should coat the back of a spoon.

Carefully remove the sticky rice bowl from the steamer with your oven mitts on. Pour half of the sauce into the bowl. Stir to mix well.

The mango sticky rice is ready to serve when the rice mixture and the sauce cool to room temperature. You can serve it or store the extra sauce and the sauce-rice mixture separately in the fridge until ready to serve, up to 3 days. The sauce will further thicken when cooled. Stir in more coconut milk to dilute the sauce if it gets too thick.

To serve, transfer the coconut rice into serving bowls or plates. Place the sliced mango on the side. Pour a few spoonful of the extra coconut sauce on top of the rice. Garnish with toasted sesame seeds, if using.

If you use refrigerated sticky rice, you can gently heat it in the microwave to bring it to room temperature before serving, for a better texture. However, it’s highly recommended to serve the rice when it’s fresh, for best results. Do not freeze the sticky rice, as it will create a very tough texture.