Put the well washed, chopped fruit (blueberries, pitted cherries or gooseberries whole!) On top with the cold water, bring to the boil and cook over a low heat for 20 minutes. Strain the fruit through a sieve (not rhubarb, leave some for cherries).
Bring the liquid back to the boil, slowly stir in the mixed cornstarch and bring to the boil again briefly. Season the soup with vanilla sugar, sugar, lemon juice (alternatively with wine or must). Serve the soup warm or cold as desired.
Tip: Use rusks, roasted bread cubes, soup macaroons, poor knights, almond rice or snow dumplings as an insert.