In a saucepan, bring the cherry juice, sugar and cinnamon stick to the boil. Meanwhile, mix the cornstarch with the water in a cup. When the juice mixture is boiling, add the mixed cornstarch and bring to the boil again. Then reduce the heat, add the drained cherries and let everything simmer over a medium heat for about 5 minutes. Remove the cinnamon stick before serving.
You can cook the cherries hot e.g., Eat with waffles or custard.