White Sauce: Melt butter on a low heat. Add flour and cook for 5 mins, stirring. Meanwhile, place milk in a pan with bay leaf and cloves and bring to just below a boil. Pour milk into the flour mix a little at a time, stirring, season and cook for 5 mins.
To finish the sauce: Melt butter in a pan and add the vegetables. Cook for 5 mins without colouring, add wine and lemon juice and reduce by two thirds. Add white sauce and cream, simmer for 2 mins, stirring continuously. Remove from heat.
Mashed potato: Cover potato with cold water, add salt. Place on heat and bring to boil, then simmer until potatoes are cooked. Drain well. Put potatoes back in the pan to dry out, then mash, adding butter, ½ tsp salt and warm milk. Once smooth, remove from heat, add nutmeg and egg yolks. Put mash into a piping bag fitted with a star nozzle.
To finish: Add the fish to the hot sauce, cook lightly for thirty seconds, then add the mussels, shrimps and chives. Divide between four pie dishes and pipe with the potato. Sprinkle with grated cheeses, place a langoustine head in the middle of each pie and bake at 180C/Gas4 for 15 mins until golden, sprinkle with chives and serve.
Recipe by appetite magazine at https://www.appetitemag.co.uk/fish-kitchen-pie/