Heat the oven to 220C/200C fan/gas 7. Tip the oil into a large, deep roasting tin and put in the oven to heat up for at least 20 mins. Peel the potatoes, then cut in half if small, or into quarters if large. Tip into a pan of well-salted cold water and bring to the boil. Boil for 8 mins until almost tender, then drain. Leave to steam-dry for 10 mins, then gently shake to fluff the potatoes up a bit.

Remove the roasting tin from the oven, crumble in the stock cube and stir carefully into the oil. Add the potatoes and gently toss to coat them, then season and toss again. Roast in the oven for 1 hr until golden, turning the potatoes a few times to ensure even browning.