1. Finely slice the onions and the fennel bulbs. Put half the olive oil in a large heavy based casserole or pan and gently fry the vegetables until soft. Add the chilli and garlic and saute for a minute until golden. Add the white wine and simmer for two minutes.
2. In a separate saucepan, bring 2 litres water to the boil and drop the salt cod filets into it. Let the water come back to a simmer for 1 minute and remove the cod immediately. Set aside reserving the water. The cod should be very lightly cooked and just flaking. Take 2 tablespoons of the water and mix with the ground saffron in a cup.
3. Pour the remaining water from the cod into the casserole with the vegetables and add the thyme and some black pepper. Bring to a simmer and add the potatoes. Cook until the potatoes are tender. The stock will reduce a bit. Now stir in the saffron.
4. Roughly chop the parsley and add to the simmering soup along with the salt cod
flakes. Add lemon juice to taste. Check for seasoning. It may not need any salt at all depending on how salty the cod is. Turn off the heat to prevent the cod flakes becoming over cooked and woolly.
5. Enrich the soup with a little more olive oil and serve whilst piping hot with Aioli and croutons or bread.