Rinse and drain the glutinous rice. Combine with the water in a heavy pot. Bring to a simmer, cover and cook on low for 15–20 minutes until the water is absorbed and the rice is tender. If the grains are chalky, add 2 tablespoons water, cover and steam a little longer.
Meanwhile, simmer the coconut milk, sugar and salt in a wide pan for 10–15 minutes, stirring, until syrupy. Reserve 1/4 cup of sauce for the top. Oil an 8-inch square dish.
Fold the hot rice into the remaining coconut mixture. Cook over medium-low heat for 8–12 minutes, stirring and scraping the bottom, until glossy and sticky enough to pull away from the sides.
Press evenly into the oiled dish. Spread the reserved sauce over the top. Rest 20–30 minutes for cleaner cuts, then divide into nine squares. Refrigerate leftovers within 2 hours.