Preheat the oven to 180℃.

Peel the potatoes and chop into halves and quarters. Put them into a pan of salted water.

Bring to the boil, and then simmer until the potatoes are tender. Drain them in a colander and leave to steam dry.

Mash the potatoes, then stir in the milk, butter and creme fraiche. Season with salt and pepper. Set it aside whilst you get the pie filling ready.

In a large saucepan melt the butter, then add the flour and cook for a further minute.

Gradually pour in the milk, continuously whisking over a medium heat. Stirring to avoid any lumps.

Once all the milk has been added, continue to cook until it has thickened.

Take it off the heat and stir in the grated cheese until it has melted.

Now add the mixed fish, dijon mustard, spring onions, sweetcorn, peas and chopped parsley. Stir until it is well combined.

Transfer the mixture into a pie dish. Dollop over the mashed potato then use a fork to rough it up on top.

Scatter the remaining cheddar over over the top, then bake it in the oven for 25 minutes until it is golden and bubbling at the edges.