Norwegian Fish Soup

Halve the leek lengthways and cut it into fine strips about 5 cm long. Cut the carrots, and the celeriac if using, into fine matchsticks. Melt the butter in a wide pan over low heat and sweat the leek, carrots and celeriac for 5 minutes, stirring so nothing takes on any colour. The soup should stay pale.

Pour in the fish stock, bring to a gentle simmer and cook for 8 to 10 minutes, until the vegetables are tender but the carrot still has some bite.

Add the double cream and simmer for another 5 minutes, uncovered; the soup stays light and pourable.

Season now, before the fish goes in: the vinegar, the sugar, then salt and white pepper. Taste and keep adjusting until it is noticeably sweet and sour rather than simply rich. This is the point where the soup either becomes fiskesuppe or stays a plain chowder.

Skin the cod and salmon fillets and cut them into 3 cm chunks. Turn the heat down until the surface is barely trembling and slide in the cod and salmon. Poach for 4 to 5 minutes without stirring, until the pieces have turned opaque and flake when pushed with a spoon.

Chop the dill. Take the pan off the heat, stir in the soured cream and most of the dill with a light hand so the fish stays whole, and check the seasoning once more.

Ladle into warm bowls, keeping the pieces of fish intact, and finish with the remaining dill.