Stone the sour cherries with a suitable device while collecting the juice. Then put the cherries with the juice in a large saucepan and pour the sugar over them. Let it steep overnight so that enough juice can form.
Bring the sour cherries with the sugar to the boil and add the pulp of the vanilla pod. Let it cook until the juice has developed into a syrup. Do a gelling test every now and then, because the syrup must not become too firm. Just before the boil is finished, add the lemon juice.
Put the cherries with the syrup in hot, but dry, glasses. Only close when the content has cooled down!
The cherries can be served with ice cream, served as a soft drink with water, as the Greeks do, or as a spread.