Place all of the vegetables excluding the potatoes into a large heavy-bottomed saucepan. Sauté in the butter, without colouring until soft, add garlic and flour and cook for a further two minutes.
Meanwhile, in a separate pan heat the fish stock. Slowly pour into the vegetables, stirring continuously, and bring to the boil.
Prepare the haddock by removing the skin and any bones and cutting into a large dice. Add diced smoked haddock, ground pepper, bouquet garni tied with string and chunky diced potatoes to pan and simmer for 20 minutes until potatoes are soft.
Stir regularly to prevent the chowder from sticking to the pan. Finish with milk and cream, and the juice of one lemon. Remove bouquet garni. Correct seasoning ( the soup is likely to be sufficiently salted because of the smoked haddock ).
In a little water steam the mussels for two to three minutes until open, remove and cool. Strain out the cooking liquor and add to chowder. You can shell the mussels in you prefer them that way.
To serve reheat with cocktail prawns and mussels, cooking for 3 to 4 minutes to totally reheat the seafood, stirring to prevent the chowder from sticking to the pan.
Ladle carefully into a bowl and top with broken salted crackers and chopped parsley.