Roughly dice the vegetables, halve the onion with the skin, press the garlic with the skin, press the fennel seeds and mustard seeds in the mortar a little. Core a small dried red chilli pepper. Wash the tomatoes and remove the stalk.
Heat the oil in a large saucepan, briefly fry the onion halves, add the fish and vegetable pieces and fry them, add the spices and fill up with cold water. Bring to the boil and simmer gently for at least 1-2 hours. Put the fish stock through a fine sieve in a saucepan and clarify with an egg white.
This fish soup is a fine base and can now be changed as desired. Adding finely cut vegetable strips and small cubes of fish fillet, a little cream, potato cubes or smoked paprika powder. There are no limits to personal preferences.
The fish base is best cooked when a whole fish is filleted.