To make the broth, heat 4 tablespoons of olive oil in a large pan over a medium heat. Add the fennel and cook for 3 to 4 minutes without it coloring, then add the red onion, sea salt, tarragon and black pepper.

Add the fish bones and offcuts and the tomatoes, then cover with water. Bring to a simmer, skimming off any residue that rises to the surface. Add the tomato purée and saffron and bring back to a simmer. Cook for about 1 ½ hours, or until it has reduced by about a third.

Sieve the broth, pressing down the contents of the sieve with a ladle to extract as much liquid as possible, then add the lemon juice and whisk in the butter. Check the seasoning, then cool and refrigerate until needed.

To make the rouille, whisk the egg yolks with the seasoning, lemon juice, saffron and cayenne pepper. Slowly add the oil in a thin stream, whisking continuously, then stir in the garlic. Add a little warm water if it’s too thick. Set aside until needed.

Bring the reserved broth up to a simmer, then add all the fish. Poach until just tender, adding the firmest fillets first, then remove and place on a serving platter. Ladle over the broth. Serve with the rouille on the side and some garlic croutons.