For the stock: Rinse the fish bones thoroughly in cold water. Remove the under shell of the crab, pull out the gills and discard, then chop the body into pieces.

Heat the olive oil in a pot over high heat and cook the fish bones and crab for a few minutes, stirring, before adding the onion, carrot, celery and parsley stalks. Cook a few more minutes until aromatic, then add wine, cook for a few minutes, then fill with just enough water to cover, add a pinch of salt and bring to the boil. Skim and reduce the heat to a gentle simmer for 30 minutes. Strain the liquid and discard the bones.

For the soup: Cut the fish into bite-sized pieces, ensuring there are no bones. Sweat the fennel, garlic and leek in the butter and olive oil until soft and pale golden.

Add the tomatoes and saffron and cook for a few minutes before adding the sherry, orange zest, bay leaf, fish stock (from previous step) and potatoes. Bring to the boil and skim the surface. Reduce heat to a simmer and cook for 30 minutes.

In a separate pot over high heat, steam the mussels open in a little olive oil and white wine, covered by a lid. Remove mussels to a bowl and add the cooking liquid to the soup. Taste for seasoning and add the fish pieces and prawns. Simmer gently until they are just cooked, about 5 minutes.

To serve

Serve immediately in individual bowls with the mussels, a sprinkle of freshly chopped parsley and a dollop of aioli.