Rinse 1 cup glutinous rice until the water runs mostly clear
Soak the rice in water for 4 to 6 hours or overnight
Drain the rice
Steam the rice over simmering water for 20 to 30 minutes until tender
Heat 1 cup coconut milk with 1/4 cup sugar and 1/2 teaspoon salt until dissolved
Mix most of the coconut milk sauce into the hot sticky rice
Let the rice rest for 15 to 20 minutes to absorb the sauce
Slice ripe mangoes
Serve the sticky rice with mango slices
Drizzle the remaining coconut milk sauce over the top
Add sesame seeds or mung beans if desired