Place beef on an oven tray, season liberally and bring to room temperature (40 minutes).
Meanwhile, for potato chips, peel and thinly slice potato lengthways into wafers, then soak immediately in water, rinse then drain and dry well with a clean tea towel. Heat a large saucepan half-filled with vegetable oil over medium-high heat to 170°C. Deep-fry potato, in batches, if necessary, until golden and crisp (12 minutes). Drain on paper towel and sprinkle with nori powder.
Heat a large frying pan with oil over high heat. Sear beef, turning frequently, on all sides until browned all over but still rare (10 minutes). Rest beef for 10 minutes before cutting into thin slices.
Meanwhile, for white anchovy dressing, combine ingredients in a bowl.
To serve, loosely roll up slices of beef and arrange on a large platter with rocket and radish. Drizzle with dressing and serve with potato chips.
