1. Preheat a conventional oven to 200ºC or a fan-assisted one to 180ºC.
2. For the chips, rub the oil over a non-stick baking tray.
3. Whisk the egg white with the black pepper, salt and chilli powder until frothy. Toss the potatoes in the egg white and pour onto the baking tray.
4. Separate the chips out and cook in the oven for 45 minutes, turning every 10 minutes. Don't be alarmed by how they look in the early stages of cooking; the chips will crisp up, so persevere.
5. Meanwhile, to make the topping for the fish, whiz together the bread, herbs, capers and lemon zest in a food processor until rough breadcrumbs form, then stir through the melted butter
6. Place the flour, beaten egg and breadcrumb mixture on separate plates. Season the flour well and then dunk each plaice fillet, flesh-side-only, in the flour, followed by the egg and then the breadcrumbs.
7. Place the fish onto a large non-stick baking tray and bake on the top shelf of the oven 12 minutes before the chips are done.
8. Don't overcook the fish. The thinner the fillet, the less time it will take to cook.
9. While the fish and chips are cooking, cover the peas with water, bring to the boil and boil for four minutes. Drain and mash the peas with the yoghurt, mint, lemon zest and juice, and season well.
10. Serve the fish and chips together with the mushy peas and a wedge of lemon.