For fish stock, fillet fish, remove pin bones and set to one side. Discard head. Portion into 8cm triangles. Place bones into a medium saucepan with eschallot, celery, water, dill stalks and peppercorns. Simmer for 15 minutes and skim as required. Strain through a fine sieve and leave to one side until required.
For seafood broth, pour olive oil into a deep saucepan. Add retained prawn shells and two marron halves. Cook on a high heat until shells are crisp and well cooked. Add eschallots, carrot, fennel, garlic and cook for 5 minutes.
Add fennel seed, saffron, cayenne and bay leaf and cook for 1 minute. Using a meat mallet, crush shells and spice mixture into a pulp.
Flambé with Pernod and half the Brandy. Add tomatoes and strained fish stock. Bring to the boil, reduce heat and simmer for 15 minutes. Strain through a fine strainer with paper filter into a clean saucepan.
For aioli, whisk yolks, mustard, lemon juice, paprika and garlic. While whisking pour oil into mixture in a thin stream until emulsified. Season with white pepper and salt to taste.
For seafood, heat olive oil in a large frying pan then add fish, prawns, and reserved marron and cook for 3-4 minutes. Add scallops and mussels, flambé with brandy, add a few ladles of seafood broth and cover with lid. Cook for 2-3 minutes, until the mussels have opened.
To serve arrange seafood into a deep bowl. Add oysters and, a few ladles of broth, a spoonful of aioli and garnish with dill sprigs.