For the stosuppa bring 1/2 l of water to a boil. In the meantime, mix sour cream and flour until no lumps are visible.
Slowly stir the mixture into the boiling water with a whisk. Then add the caraway seeds and season with salt.
For the mashed potatoes, boil and peel the potatoes. Mash them in a pot with the milk and stir with butter.
Pour the mashed potatoes into the stosuppa with a piping bag and serve.