In a heavy bottomed pot add olive and heat. Add half the chopped onion and garlic. Sauté without allowing it to colour.
Add the washed, cleaned clams and mussels. Add the white wine and cover with a lid. Steam clams until they just open.
After 4-5 minutes, once all the clams and mussels have opened, strain and reserve the cooking liquor/stock. Discard any of the unopened shellfish and allow the rest to cool.
Remove mussels and clams from shells and chop.
In medium pot add diced bacon and cook until brown and crisp.
Add celery, carrot, the remaining onion and garlic. Cook until soft but without any colour.
Add diced Rooster potatoes and flour (If you would like to leave it gluten free then leaver out the flour and reduce the cream for a little longer, or add 1 extra potato). Cook for 3 minutes.
Add reserved shellfish juice, (leave a little as the grit will have settled in the bottom), the fish stock and the cream.
Simmer until potatoes are tender. Add diced mixed fish, such as salmon, monkfish, hake, cod, haddock or whatever fish you would prefer. Heat through without breaking the fish and finally add the chopped mussel and clam meat, parsley, dill and mustard.
Season with salt and fresh ground pepper. Finish with a squeeze of lemon juice.