Mix one tablespoon of corn starch with two tablespoons of cold water in a small bowl until fully dissolved. Set this slurry aside.

In a medium saucepan, combine the fresh blueberries, sugar, and 1/2 cup of water. Place the pan over medium-low heat and allow the mixture to simmer gently.

Once the blueberries have softened and the mixture begins to thicken slightly, stir in the cornstarch slurry. Continue cooking and stirring frequently for about 20 minutes until the liquid becomes syrupy.

Remove the saucepan from the heat. Let the syrup cool for approximately five minutes; it will thicken further as it cools.