Heat the oven to 220C / 200C fan with a roasting tray and the oil already inside — the oil must be shimmering before the potatoes go in.

Cut the potatoes into large, even chunks and boil in well-salted water for 8-10 minutes, until a knife enters the outer centimetre easily but the middle resists.

Drain thoroughly and leave in the colander for 2 minutes to steam dry.

Put the lid on the empty pan, return the potatoes, and shake hard 3-4 times. The surfaces should look scuffed and floury.

Tip carefully into the hot oil, turn to coat, and spread out so none touch. Roast 30 minutes without disturbing.

Turn, add the smashed garlic and rosemary, and roast 15-20 minutes more until deep golden. Salt the moment they leave the oven.