Soupe de poisson

Method

1. Heat the olive oil in a large pan over a medium heat, then add the onion, leek, celery and fennel. Cook, stirring often, until softened but not coloured. Add the garlic, saffron and chilli, then cook for 5 minutes more or until fragrant. Pour in the pastis/vermouth and bubble briefly until the raw alcohol smell disappears.
2. Add the tomato purée and bubble for 2 minutes, then add the passata with some salt and the bouquet garni, stir to combine and cook for 5-8 minutes. Pour in 2 litres cold water, add the fish heads, skeletons and fillets, stir together and bring
3. to a gentle simmer. Cook, without stirring, for 2-2½ hours until the fish has completely broken down and the liquid has reduced by almost half.
4. For the rouille, either hold the chilli directly in the flame of a gas hob until blistered all over or put it under a hot grill. Once blackened, put in a plastic bag or bowl covered with cling film for 5 minutes. The skin should peel off easily. Discard the seeds, then roughly chop.
5. To make the rouille, put the chilli, vinegar, egg yolks, garlic and some salt into a food processor or mixing bowl. Either whizz in the processor or beat with an electric hand mixer until combined and starting to pale. With the motor running, carefully trickle some oil into the mixture. Don’t add it too quickly or the mixture won’t thicken. After about a minute, it should thicken into mayo; if it doesn’t, stop adding oil and whisk until it does.
6. Still processing/beating, slowly add the rest of the oil (if the rouille starts to look greasy, add a splash of water). Once all the oil has been added, beat in the breadcrumbs and the saffron with its soaking water, then taste. The rouille may need more salt or a squeeze of lemon juice. Cover and set aside.
7. Pour the cooked soup, in batches, through a fine sieve into another pan, pressing it through with the back of a metal spoon (or you can use a food mill if you have one). Discard the remaining solids. Heat until steaming, then add a final glug of pastis/vermouth. Taste and season, adding lemon juice and salt if needed. The flavour should be rich and intense.
8. To serve, ladle the soup into bowls and sprinkle with grated gruyère. Serve with bowls of rouille and toasted baguette, encouraging people to spread the rouille on the toast before dipping it into the soup.