Cut the carrots into slices about 5 mm thick. Cut the potatoes into medium-sized cubes. Finely dice onion. Heat oil in a frying pan. Sauté onion in it. Add the potatoes and carrots, pour on the stock, bring to the boil and cover the vegetables and cook over medium heat for about 10 minutes.
In the meantime, wash the fish, dab dry and cut into medium-sized cubes. Season with salt and pepper. Wash dill, dab dry, pluck flags from the stalks and chop finely, except for a little to garnish. Add the fish cubes to the vegetables, cover them and let them simmer at low heat for 3-4 minutes. Mix sour cream and some vegetable binding agent, stir carefully into the stock and bring to the boil again briefly. Fold in capers and dill, season to taste with salt and pepper and serve garnished with the remaining dill