Marseille Fish Soup

Preheat the oven to 220°C (200°C fan). Pat the whole fish and carcasses completely dry with kitchen paper. Roughly chop the whole fish through the bone into large chunks using a heavy knife or cleaver. Prepare all vegetables, garlic and aromatics. Steep the rouille saffron in warm water for 10 minutes. Mix the fine sea salt, black pepper and cayenne together.

Spread the fish pieces and carcasses in a single layer across two large roasting trays. Drizzle with 2 tbsp of the olive oil and roast on the top shelf for 25 minutes, until the fish is deeply golden and beginning to char at the edges.

While the fish roasts, heat the remaining olive oil in a large, heavy-based pot over medium heat. Add the onion, celery and fennel and cook, stirring occasionally, for 12 minutes until completely softened and beginning to colour.

Add the smashed garlic, tomato paste and chopped tomatoes to the pot and stir well. Cook for 5 minutes until the tomato paste darkens slightly and smells sweet.

Pour in the white wine and scrape up any caramelised bits from the base of the pot. Cook for 3 minutes until the wine reduces by half.

Add the roasted fish and all their roasting juices to the pot. Pour in the fish stock, add the saffron threads, orange zest and bouquet garni, and bring to a vigorous boil over high heat.

Reduce the heat to a lively simmer and cook uncovered for 30 minutes, pressing down on the fish pieces occasionally with a wooden spoon to encourage them to break apart.

Remove the bouquet garni and orange zest. Working in batches, pass the entire contents of the pot through a food mill or coarse sieve fitted over a large clean pot, pressing very firmly to extract every last bit of flesh and juice — this step creates the characteristic thick, rust-coloured broth. Discard the solids.

Return the strained soup to medium heat, stir in the pastis, and taste. Adjust seasoning with the salt and cayenne mixture. Bring back to a gentle simmer and keep warm. Use a meat thermometer to confirm the soup reaches 75°C throughout before serving.

Make the rouille: pound the 4 garlic cloves with the coarse salt in a mortar until a smooth paste forms. Transfer to a bowl, add the egg yolk, saffron with its soaking water, and Dijon mustard, and whisk together. Add the olive oil drop by drop at first, whisking constantly, then in a thin stream until you have a thick, glossy emulsion. Season with lemon juice and a pinch of salt. Refrigerate until needed.

Toast the baguette slices under the grill for 2 minutes per side until deeply golden and crisp.

Ladle the hot soup into warmed bowls at the table. Serve the croutons, rouille and grated Gruyere separately so guests can spread rouille onto the croutons, float them on the soup, and shower with cheese.