How to Make It
Mix the olive oil, garlic, saffron, lemon zest, salt, pepper, fennel seeds, herbes de Provence, onion, celery and carrot in a large bowl. Add the chicken and turn to coat. Cover and refrigerate until you are ready to cook.
Transfer the contents of the bowl to a large saucepan. Add the tomatoes, wine, water and potatoes. Cover and bring to a boil over high heat. Reduce the heat to low and simmer gently for 25 minutes. Add the sausage and cook for 5 minutes longer. If adding Pernod, stir it in now with the tarragon.
Transfer 2 of the cooked potato quarters and 1/4 cup of liquid from the saucepan to a food processor. Add the garlic, cayenne and paprika; process for 10 seconds. Add the egg yolk. With the processor on, pour in the olive oil, and process for a few seconds, until incorporated. Season with the salt.
Serve the bouillabaisse in warm soup plates with a spoonful of the rouille drizzled on top.