Wash and clean the fennel and remove the green stalks. Cut the fennel into thin slices. Put the fennel green aside. Peel and wash the carrots and cut them into thin slices. Wash and clean the tomatoes and cut them into medium-sized pieces.
Peel and finely chop the onion. Heat the oil in a pot and sauté the onion in it. Add tomato paste, sauté briefly and deglaze with Noilly Prat. Fill up with vegetable stock. Add fennel, carrots and tomatoes and simmer for about 15 minutes.
In the meantime, wash the salmon fillet, cod fillet and prawns and pat dry. Cut salmon and cod into medium sized pieces. Season vegetable stock with salt and cayenne pepper. Bring to the boil, reduce heat.
Add the fish pieces and prawns and cook for about 5 minutes. Arrange the fish and vegetable soup in a terrine and garnish with the fennel green. Serve with a dash of crème fraîche if desired.