Bring just under 1 litre/1½ pints/3¾ cups of water to the boil and add salt, the bay leaves, half the parsley root or parsnip, a few crushed peppercorns and half an onion. Add the fish, and simmer for 10 minutes. Then transfer the fish to a heatproof serving dish, and cover with 2 finely chopped onions, the remaining grated parsley root or parsnip, half the black pepper, the parsley, dill, fennel seeds and half the saffron or turmeric. Sprinkle with salt and pour the sour cream over all. Set this to cook very slowly, either on the stove or in a steamer for about 10–15 minutes.
In another pan, soften the remaining onion and the carrot, both finely chopped, in the oil. Strain the fish bouillon into the pan, bring it to the boil and add the rice. Let it come back to the boil on a medium heat. Add the remaining pepper and saffron, stir, cover, and cook on a very low heat for 8–10 minutes. Remove from heat and leave the rice to rest, still covered, for 5 minutes.
Serve the rice, sprinkled with lemon juice, in a bowl, and the fish on the dish on which it was cooked.