To cook the chips, put them in a sturdy saucepan that holds them in a double layer and still has plenty of space above them. Pour over enough cold oil to cover them by about 2cm. Put the pan on a high heat and bring the oil to the boil, stirring the chips with a wooden spoon occasionally so they don’t stick.
After about 20 mins the oil will clear and the chips will look like they are frying. Keep an eye on them, stirring with the spoon occasionally until golden and crisp. Scoop them out with a slotted spoon into a dish lined with kitchen paper, and season with flaky sea salt. Serve with the steak.