Heat the oil in a large saucepan and add the onion, garlic and leek, cover and cook gently for five minutes, stirring occasionally until the vegetables are soft
Pour in 4 cups of water, the tomatoes, herbs, saffron and pasta.
Season with salt and ground black pepper and cook the 15 to 20 minutes
Scrub the muscles pull off the "beards". Discard any that will not close when Sharpley tapped
Cut the fish into bite-size chunks and add to the soup, placing the muscles on the top.
Simmering with the lid on for 5 to 10 minutes until the matter was open and the fish are just cooked
Discard any unopened mussels
To make the rouille, pound the garlic, can pimiento and bread crumbs together in a pestle and mortar (or you can use a blender or food processor). Stir in the mayonnaise and season well
Spread the toasted French bread with the rouille and serve with the soup.