Cut fish into 3 cm cubes.

Heat oil in a large saucepan.  Add onion, garlic, tomatoes, leek, fennel, thyme, bay leaf and orange peel.  Gently saute 8 minutes, mixing well.

Stir in boiling water and boil 5 minutes; this is to allow the oil and water to form an emulsion, giving a smooth sauce.

Add cubed fish and simmer 10 minutes.

Add saffron, if desired, and season to taste.  Add whole shellfish and simmer until these open 1-2 cm.  Discard those shellfish that do not open.

Serve in large soup bowls.