For the seafood hotpot
Heat 2 tbsp olive oil in a large casserole dish set over a medium heat.
Add the fennel, celery, carrot, red pepper, and a pinch of salt, sweating for 6-7 minutes until softened.
Add the white wine, let it reduce by two-thirds, and then stir in the stock and saffron if using. Bring to a simmer and then reduce heat to low.
Arrange the mussels, clams, and calamari in the broth.
Cover the pan with a lid and cook over a low heat for 8-10 minutes until the mussels and clams have opened; discard any that don't.
Meanwhile, heat the remaining olive oil in a large saute pan set over a moderate heat.
Season the fish pieces with salt and pepper and then fry in the hot oil until golden on both sides.
Transfer to the broth and keep covered over a low heat.
Season the prawns and then sauté in the remaining oil in the saute pan until pink on both sides.
Place the prawns in the broth and continue to cook over a very low heat for a further 5 minutes.
Adjust the seasoning to taste.
To serve the seafood hotpot
Ladle the hotpot into shallow bowls.
Serve with a sprinkling of parsley on top and some lemon wedges on the side for squeezing over.