Heat oven to 200C/fan 180C/gas Tip the potatoes into a large pan of boiling water, wait for the water to boil again, then cook for 5 mins. Drain, tip back into the pan and shake well to rough up the edges a little. Tip onto a baking tray, toss with the lemon zest, oil and some flaky sea salt, then roast for 30 mins until golden and crisp.