First wash the potatoes very thoroughly, then dry in a clean tea cloth – they need to be as dry as possible; if they're ready-washed, just wipe them with kitchen paper.
Leaving the peel on, slice them in half lengthways and then cut them again lengthways into chunky wedges approximately 1 inch (2.5 cm) thick. Dry them again in a cloth, then place them in a large bowl with the oil and a sprinkling of salt. Now toss them around a few times to get them well covered with the oil, then spread them out on the baking tray and place in the oven on a high shelf to roast for about 30 minutes.
They should be golden brown and crisp after this time; if not, give them a few more minutes. Finely sprinkle with a little more salt, then serve absolutely immediately.