Rinse and soak the glutinous rice for at least 6 hours or overnight.
Drain the rice and steam it using your preferred method (traditional steamer, Instant Pot, or rice cooker) for 25 to 30 minutes.
While rice steams, heat 1½ cups coconut milk with ⅓ cup sugar and ½ teaspoon salt. Stir until sugar dissolves. Keep warm.
While both are hot, gently mix the steamed rice and coconut syrup. Let it sit covered for 15 to 20 minutes to absorb.
In a saucepan, heat ½ cup coconut milk, ¼ teaspoon salt, and 1 teaspoon sugar. Add cornstarch slurry if you want it thickened. Stir until slightly thick.
Place sticky rice on plates, top with mango slices, drizzle salted coconut sauce, and garnish with sesame seeds or mung beans.
