Step 1

For the mash, put the potatoes in a pan of salted water, bring to the boil, then reduce the heat and simmer for 20 minutes or until tender.

Step 2

Drain the potatoes and let them sit in the colander for a few minutes, then return them to the pan. Mash until smooth, then beat in the butter and milk. Season and set aside.

Step 3

Meanwhile, heat the oven to 180°C/160°C fan/gas For the filling, pour the milk into a large saucepan and bring to a simmer. Melt the butter in another large saucepan, then add the flour and cook, stirring, for 1-2 minutes; don’t let it brown. Gradually whisk in the hot milk, then bring to a simmer and cook over a low heat for 20 minutes, stirring occasionally.

Step 4

Take the pan off the heat and stir the spring onions, capers, mustard and parsley into the sauce. Season with salt and pepper, then add the fish and stir gently to combine.

Step 5

Tip the fish mixture into a large baking dish, then spoon or pipe the mashed potatoes on top. Scatter over the grated parmesan.

Step 6

Put the dish on a baking sheet and bake for 25-30 minutes until piping hot and golden on top. Serve straightaway with a tomato and cucumber salad or buttered leeks tossed with a little mint. This recipe is from Nathan Outlaw’s cookbook Nathan Outlaw’s Home Kitchen (£20, https://www.waterstones.com/book/nathan-outlaws-home-kitchen/nathan-outlaw/9781849499606 >Waterstones)