Heat the oven to 230C/210C fan/gas 8. Put a rack on the bottom shelf of the oven to heat up. Pour the rapeseed oil into a roasting tin and put on the middle shelf to heat up. Meanwhile, cut the potatoes into 1cm-thick slices, then into 1cm-thick chips. Tip the chips into a large saucepan, pour over the vinegar and season with 2 tsp fine sea salt. Top up with water until the chips are fully submerged. Set the pan over a high heat and bring to the boil, cooking for 5 mins until the edges of the chips are tender. Drain well and leave to steam-dry in the colander for 10 mins. Will keep chilled for up to a day.

Sprinkle the cornflour over the chips and gently toss to combine using your hands. Carefully tip the chips into the hot oil in the roasting tin, shake into an even layer and bake for 30-40 mins until golden and cooked through.

Heat the olive oil in a non-stick pan over a medium heat, stir in the panko and cook until lightly browned, about 4 mins. Tip the panko into a bowl and stir in the lemon zest and parsley. Pour the flour into a shallow, wide bowl and season well. Whisk the eggs and mustard together in another wide bowl. Pat the fish fillets dry, then dip into the seasoned flour, then the egg mixture, then finally the panko to coat. Arrange the fish, well spaced apart, on an oiled rack over a second roasting tin. Move the chips to the lower shelf of the oven and put the fish at the top. Cook for 10-15 minutes until the fish is crisp on the outside and cooked through.

Meanwhile, for the dill mayo, combine all the ingredients in a bowl. Season well and chill until needed. Will keep, covered and chilled, for up to two days. Cook the peas in a pan of boiling water for 2 mins until tender, drain and immediately plunge into a bowl of cold water to halt the cooking process. Leave to cool for 5 mins, then drain again. Melt the butter in a saucepan over a medium heat and cook the lemon zest for 1 min until fragrant. Tip in the peas and lightly crush with the back of a spoon (you want to retain some texture), then stir in the mint, along with some lemon juice and seasoning to taste. Serve the fish, chips and peas with the dill mayo on the side.