Keeping aside all bones, cut the fish into bitesize pieces, roughly the size of the scallops. The monkfish tail ought to have a great piece of bone for the stock.
Next, cut all the vegetables to about 2.5cm/1" in size and set aside.
Heat the olive oil in a large saucepan on low heat and sauté the vegetables for about 10 minutes until they are soft and fragrant. Stir frequently to avoid browning.
Increase the heat to high and add the water and all the fish bones and shells, the saffron and half a tsp of salt.
Bring to boil and then simmer, uncovered, for 20 minutes.
With a skimmer or a ladle, remove any large pieces of bones and shells, then strain the whole lot into a clean saucepan, pressing down on all the vegetables to get all that delicious goodness into your broth.
Place the broth on medium heat and add the cider and bring to boil.
Add all the fish and shellfish, including the langoustines, bring back to boil, then lower heat and simmer to cook the seafood for about 5 minutes, until everything is cooked through.
Place 2 tbsp of aioli in a cup and add 1 ladleful of the soup and mix to lighten the aioli.
Pour this mix back into the soup and stir gently but thoroughly to mix it all in and thicken the soup.
Season with freshly ground black pepper and check seasoning. Add some more salt if needed.
Divide equally into 4 four bowls, topping each with a langoustine and some dried chilli flakes and parsley.
Serve immediately with a side helping of more aioli, for everyone to add to their soup if they want, and with lots of crusty bread or even garlic bread to mop up all that delicious soup.