Wash and sort the blueberries. Add them to a pan with about the water and let them simmer gently until they burst.
Now add the sugar, stir, and let it simmer for another 5-10 minutes.
In the meantime, dissolve the cornflour in a little cold water until it is lump-free.
Remove the pan from the heat and slowly stir in the dissolved cornflour. Bring it back to a brief boil and then remove the pan from the heat.
Serve the blueberry soup warm with bread or biscuits and a dollop of whipped cream or ice cream. You can also let it cool, place it in the fridge, and serve it cold.