Stir together coconut milk, sugar, and salt in a saucepan. Spoon 3 to 4 tablespoons coconut milk mixture into a small bowl and stir in cornstarch until dissolved; pour into the saucepan. Bring mixture to a boil while stirring constantly; cook until smooth and thick, about 5 minutes.

Pour into molds, cover each with plastic wrap, and refrigerate until cold and firm, 3 hours to 2 days.

Run a thin knife around the edges of each mold; invert onto serving plates. Garnish tops with cinnamon.