Place the potatoes in a large pan of cold, salted water with the herbs. Bring the water to the boil and simmer gently for 8-10 mins until the potatoes are cooked through but not about to collapse. Gently drain the potatoes in a colander, but don’t shake or ruffle up. Leave to drain and cool. If making ahead, place on a tray in a single layer and leave in the fridge, uncovered, until ready to roast. Can be made up to two days ahead.
Heat oven to 200C/180C/gas 6. Pour the oil into a deep roasting tin (the oil should be about 0.5cm deep) and put in the oven for 5 mins. Remove from the oven and gently tip the potatoes and herbs into the oil. Use a spoon or spatula to turn the potatoes until they’re completely coated in oil, then return the tin to the oven and roast for 40 mins.
Remove from the oven and turn the potatoes in the oil again. Return to the oven for 20 mins, then turn the potatoes in the oil once more. Turn the oven up to 220C/200C fan/gas 7 and cook for a final 20 mins, or until golden and crunchy. Sprinkle with a little sea salt to serve.