Rinse the glutinous rice until the water runs clear, then soak for 30 minutes. This is the quiet work that makes the magic happen.
Drain and cook the rice with the 1 1/2 cups of water. If you have a steamer, steam until tender; if not, a covered pot on low heat works too. The goal is tender, not porridge.
Meanwhile, whisk coconut milk, sugar, and salt in a small saucepan. Warm gently until the sugar dissolves; do not boil. You want a silky sauce, not a caramel disaster.
Fold about two-thirds of the coconut sauce into the cooked rice while it’s still warm. Let it rest for 10–15 minutes, so the flavors can mingle and the rice can drink up the goodness.
Slice mangoes into attractive pieces. You’re about to serve sunshine; don’t skip the plating drama.
Serve rice warm or at room temperature, topped with the sliced mango and a drizzle of the remaining coconut sauce. Sprinkle sesame seeds if you’re feeling fancy.