in a saucepan, add 3 1/2 cups fresh blueberries, 1/2 cup granulated sugar, 1 teaspoon cornstarch, 2 tablespoons water, and 1 tablespoon lemon juice. stir just to combine. cook the blueberries over medium-low heat for about 10-15 minutes or until it begins to thicken. remove it from heat and let it cool down.