Heat a deep-sided frying pan until hot and add a tablespoon of olive oil. Add the carrot, onion, fennel, two of the chopped garlic cloves, the chilli flakes and fennel seeds and fry gently for 2-3 minutes.
Drain the mushrooms and squeeze out any excess liquid, then roughly chop. The soaking liquid can be used in another dish.
Add the chopped porcini to the pan along with the tomatoes and cook over a low-medium heat for 20 minutes, or until the tomatoes have broken down and the vegetables are softened.
Add the fish stock and bring to the boil. Reduce the heat and simmer for 20 minutes.
Meanwhile, place the potatoes into a saucepan of boiling water along with the saffron and cook for 5-8 minutes, or until just tender. Drain and set aside.
Remove the fish broth from the heat, then either use a stick blender or pour into a blender and blend until smooth. Season, to taste, with salt and freshly ground black pepper.
Heat a shallow pan until hot, then add the remaining tablespoon of olive oil. Add the clams, red mullet, monkfish and white wine, cover with a lid and cook for 1-2 minutes, shaking the pan from time to time.
Remove the lid and discard any clams which have not opened.
Add the fish broth and saffron potatoes and bring to the boil. Reduce the heat and simmer for a few minutes, then add the cooked lobster, if using, and continue to simmer until heated through.
In a bowl, mix the chopped parsley with the remaining chopped garlic. Sprinkle the mixture over the top of the stew and serve.