1 cup water
1 cup sugar
1 tablespoon lemon juice, freshly squeezed
1 tablespoon cornstarch
1/2 teaspoon vanilla extract
Place blueberries, water, sugar, and lemon juice in small pan. Cook it, stirring occasionally, in medium heat. Let it come to a boil. In the mean time, mix cornstarch with 1 tablespoon water in a small bowl. Slowly stir in the cornstarch into the pan. Let it simmer for 5 minutes or until it is thick enough to coat the back of a wooden spoon. Take it off the heat and stir in the vanilla. Store it in an airtight jar in the fridge.