Bring the potatoes to a boil from cold water and then simmer until soft.
When cooked, drain the potatoes and mash with a splash of milk and a tbsp of butter. Season with salt and pepper.
In a new saucepan, add 30g butter and 30g plain flour and heat gently until the butter has melted, stirring regularly. Cook for 1-2 mins.
Gradually whisk in 400ml milk and bring to the boil, stirring to avoid any lumps and sticking at the bottom of the pan. Cook for 3-4 mins until thickened.
Take the sauce off the heat and stir in 400g mixed fish, 1 tsp mustard, fresh herbs, sweetcorn and peas. Spoon into your oven dish or 6-8 ramekins.
Spoon the mash potato on top and sprinkle with a handful of grated cheddar cheese (optional)
Bake the fish pie in the oven for 30 minutes or until golden and bubbling at the edges. I serve mine with added vegetables and refrigerate the leftovers if needed.
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