This is such an easy recipe that always turns out well, whether you use frozen berries or fresh ones. I've swapped the granulated sugar in the original recipe for a little honey. The traditional Swedish recipe calls for 3-4 tablespoons of sugar if you prefer.
Rinse fresh blueberries in cold water before you start.
In a medium pot, bring the water, honey, (or sugar) to a boil over a medium heat.
Add the blueberries and simmer for 2-3 minutes until soft. If using frozen berries, it will take a few minutes longer. Add the vanilla essence and use an immersion blender to make a smooth soup if you prefer
Mix a tablespoon of cornstarch or potato flour with a little water and add to the soup.
Bring to a gentle boil to thicken the soup, stirring continously, and remove from the heat.
Notes
Serve on its own either chilled, at room temperature or hot. It's common in sweden to add a splash of cream, some whipped cream, ice cream, plain yogurt, or sour cream. Delicious served chilled in summer with a splash of lemon juice or a little lemon zest and a sprig of fresh mint. You can also serve blueberry soup with cottage cheese and some chopped and toasted nuts for a more filling snack.