In a large pot melt the butter, add the onion, leek and celery, lower the heat to a simmer and sweat until soft but not coloured.
Add the garlic and seasoning, then stir in enough flour to make a roux - you may not need all the flour. Heat the milk in another pot with the bay leaves and add slowly to the roux, stirring well to avoid lumps. When it is smooth, add the marinara, fish offcuts, lemon juice, fish sauce, and fish stock. Stir well and simmer on low heat, adding grated potato to taste. Simmer slowly, keep stirring until there is no taste of flour and the seafood flavor has developed well.
