Preheat your oven to 200°C.
Pulse walnuts, chives, garlic, breadcrumbs, and butter in a food processor until crumbly.
Coat the lamb with 15ml of oil and press the crumb mixture onto one side.
Fry the lamb in an ovenproof pan with the remaining oil for 4 minutes.
Roast the lamb in the oven for 10 minutes until the crust is golden.
Slice a flat base on each potato and make several vertical incisions on top.
Drizzle potatoes with oil and season with salt and pepper.
Roast potatoes on a baking sheet for 15 minutes until golden and crisp.
Serve the lamb steak alongside the hedgehog potatoes.