Firstly, pour the cranberry juice and sugar into a saucepan and bring to the boil.
While it is boiling, mix the potato flour with the water and stir well (you can also use corn starch instead of potato flour). Pour the mixture into the saucepan.
Let it simmer until it bubbles, finally adding some raspberries and lingonberries. The berries will release delightful color and taste to the Kiesel.