Rinse 1½ cups glutinous rice in a fine-mesh sieve under cold running water until water runs clear; transfer rice to medium bowl, fill with cold water to cover by 1", and chill overnight.

Drain rice well in a fine-mesh sieve. Set sieve over a large deep saucepan of simmering water (sieve should not touch water). Cover with a kitchen towel and lid and steam rice 30–40 minutes, or until tender.

While rice is cooking, bring 1 cup well-stirred canned unsweetened coconut milk, ⅓ cup granulated sugar, and ¼ teaspoon kosher salt to a boil in a small saucepan, stirring regularly, until sugar is dissolved. Remove from heat and keep mixture warm.