Wash the fish thoroughly, clean if necessary, dry on paper towels, cut into medium pieces. Wash and peel the vegetables. Grate 1 carrot on a medium grater, cut the white part of the leek into thin half rings, and the greens into large pieces. Leave 2-3 potatoes, cut the remaining ones into cubes.
Cook the broth. Place fish, onion, 1 carrot, leek, bay leaf, peppercorns in a saucepan. Fill with water, add salt, and place on medium heat. After boiling, add 2-3 potatoes; they can be cut in half. After 20 minutes, turn off the heat, strain the broth, and mash the potatoes.
Prepare the roast. Melt the butter in a preheated frying pan, add grated carrots and leeks cut into rings, fry until golden brown for 7-8 minutes.
Cook the soup base. Pour the strained broth into a saucepan, place over medium heat, and bring to a boil. Then add the chopped potatoes and a sprig of thyme. After boiling the broth with potatoes, add pieces of fish and cook for 15-20 minutes.
Prepare the creamy base. In a deep bowl, combine mashed potatoes, frying and cream, stir.
Combine the bases and finish preparing the soup. Place the cream and vegetables into the saucepan with the soup, stir, reduce the heat to low and simmer for 2-3 minutes.
Pour “Lohikeitto” into deep serving plates and serve hot.