Wash fish heads really well. Place in the pot. Cover with water and add bay leaf. Add salt, pepper and white pepper. Bring to a boil and simmer for 20 minutes. Remove fish and set aside.
Bring broth back to boil. Add cubed potatoes. Simmer for 10 minutes.
Meanwhile melt butter in a small skillet. Add finely chopped onion and shredded carrot. Saute for 5 minutes, add chopped tomatoes, garlic and cook for another few minutes (with closed lid).
Scoop vegetables into the pot. Add cubed salmon fillet if using and simmer for another 10 minutes. Meanwhile separate any fish from fish heads.
Turn the burner off. Add fish to the pot along with chopped dill and heavy cream. Add fish sauce if using and serve hot.
