A creamy soup with chunks of fish and small pieces of vegetables. The broth is thickened with yogurt which not only makes it creamy but also provides tang that goes beautifully with the fish.
Place the fish, onion, garlic and peppercorns in a pan.
Pour in about four cups of water. Add salt. Bring to the boil, lower the heat, cover and simmer for about 20 minutes.
Strain the broth and cool the fish.
Heat the butter, add the onion, carrot and celery; cook gently over medium heat for about two minutes.
Add the potatoes.
Pour in the broth. Season with pepper. Taste and if it needs more salt, add some. Bring to the boil, lower the heat, cover and simmer for about 15 minutes.
Meanwhile, pick the flesh, gelatinous skin and eyes (minus the eyeballs and the soft bone that surrounds them) from the cooked fish, and break into small pieces.
When the vegetables are done, pour in the yogurt. Stir. Taste and adjust the seasonings if needed.
Add the fish, simmer for about two minutes, taste one last time and make adjustments if necessary.
Ladle the soup into bowls, sprinkle with sliced scallions and serve hot.