Divide the fish and prawns between the gratin dishes.
Heat the milk in a saucepan, over a medium heat, until it comes to a simmer then turn off the heat and transfer the milk to a jug.
Add the butter to the pan and heat until melted then tip in the flour and stir to combine for 1 minute.
Pour in a quarter of the milk to the pan, stirring all the time as the sauce comes together then add the rest of the milk.
Cook stirring until the sauce comes to a simmer and thickens, then cook for a further minute.
Take the sauce off the heat and add the pepper, half of the cheese and chives. Stir to combine and check the seasoning.
Divide the sauce evenly between the dishes and sprinkle with the remaining cheese.
Put the dishes on a baking tray and cook for 20 minutes until golden and bubbling.
Notes
Disclaimer:The nutritional information provided is approximate and is calculated using online tools. Information can vary depending on various factors, but we have endeavoured to be as accurate as possible.