Peel and quarter the potatoes lengthways. Place them in a pot of cold water with the onion, garlic, rosemary and a few grindings of salt. Bring to a boil, then turn down the heat and simmer until just cooked but still firm.

Drain well in a colander and leave for a few minutes to allow excess moisture to steam off. Swirl the colander around to roughen the edges of the potatoes – this will give you a crispier finish.

Place the whole colander over a roasting tray and slowly and evenly pour over the oil so that most of the oil goes on the potatoes. Any excess is caught by the roasting tray. Once again swirl the colander around so that the potatoes are evenly coated by oil.

Tip onto the roasting tray in a single layer, pop into a preheated oven (200ºC) and roast for one hour until deliciously browned and crispy. Shake them around once or twice during cooking to ensure even cooking. Remove from the oven, season with salt and serve immediately.

Tip: For added flavour, roast in the same oven as roast chicken or roast lamb so that the aroma permeates the potatoes.