Start by making the cherries. Put them in a small saucepan with the caster sugar and lemon juice. Cook over a medium heat for 4-5 mins until softened and breaking down, releasing a lot of their juices. Pour roughly 2 tsp of the cherry liquid into a small bowl. Stir through the cornflour to make a smooth liquid, then pour into the cherries. Bring to the boil, so the syrup thickens slightly, then remove from the heat. Will keep, covered in the fridge, for up to four days.
