For the fish stock (for 800 ml), wash 600 g of bones and skin (e.g. from skrei). Put 1 finely chopped onion, 75 g leek, 1 stalk of parsley, 1 bay leaf and 1 teaspoon of peppercorns and salt in a pot.
Pour on 100 ml dry white wine and 800 ml cold water. Bring to the boil slowly at low to medium heat. This is the only way to keep the stock clear. Skim off the resulting foam and simmer for 20-30 minutes, then sieve.
Clean, wash and cut the leek into rings. Peel and wash carrots and potatoes. Halve carrots lengthwise and cut into slices. Dice potatoes. Boil up milk, fish stock and thyme in a large pot. Add carrots and potatoes and cook for about 8 minutes.
In the meantime, rinse fish, pat dry and cut into cubes. Stir potato flour and cream until smooth. Stir into the soup, bring to the boil again and simmer for about 1 minute.
Add the fish and leek to the soup and simmer at low heat for 6-8 minutes. Wash the dill, shake dry and chop coarsely. Season soup with salt, pepper, sugar and paprika. Serve and sprinkle with dill.