Chop the onions, carrots and salted cucumbers into 1cm (about 1/2") squares, keeping the cucumber separate.
Chop all the fish into bitesize pieces, about 2.5cm (1").
Heat the oil in a pan over medium heat and sauté the onions and carrots for 5 minutes.
Add the salted cucumbers, bay leaf, black peppercorns and tomato purée, stir, and cook for 1 minute.
Add the fish stock and bring to a boil. Lower the heat right down and simmer for 10 minutes.
Add the fish, olives and capers and cook for about 3 minutes, until the fish is cooked.
Add the lemon juice and white wine vinegar, stir and taste the seasoning. It shouldn't need any salt but if you think it does, add a pinch, or as needed. Turn the heat off.
Take 1 tablespoon of smetana or crème frâiche, lighten with a little bit of the soup in the ladle or in a small bowl. Mix thoroughly, then pour back into the soup in the saucepan, and mix, VERY GENTLY, as we don't want to break the fish up. Finish off with some freshly ground black pepper.
Serve with the chopped dill and a spoonful of smetana or crème frâiche, with some fresh bread.
Video
Notes
The serving size indicates 4 as a main course, or 8 if you are serving it as a starter.