Take 50 g/2 oz (2 tbsp) of berries to prepare 1 serving of kissel (200 g/7 oz), pick over and scald with boiling water, then mash berries with a wooden spoon. Transfer mashed berries into a cheese cloth and squeeze 1 tsp of juice. Keep juice in a cool dark place. Put squeezed berries into a pot and add 1 cup of hot water, bring to boil, then strain. Cool 1/4 cup of strained liquid and dissolve 2 tsp of potato starch in it. Add 3 tsp of sugar to the remaining berry broth and bring to boil. When the liquid comes to boil add to it dissolved potato starch and return everything to boil stirring all the time. Immediately transfer to a ceramic cup and continue to mix to prevent forming of a film on top of kissel. When kissel cools down slightly — add juice squeezed from berries to it.
Kissel should be cooked in an enameled pot (without any cracks in the enamel). Potato starch should be dissolved in berry broth, not water.
Any fresh berries could be used to make kissel following these instructions.