I was dismayed to read, in Xanthe Clay's column in the Telegraph, that sunflower oil gave "a distinctly chip shop flavour" to roast potatoes, and was "to be avoided". I like potatoes roasted in lard, dripping, duck fat or goose fat, but I do not always have these ingredients, and am perfectly happy to use sunflower oil instead. The potatoes are crisp; the oil is unassertive. (The only time when I dislike the flavour of sunflower oil is, for some reason, when it has been used to fry sausages.)
As for that alleged chip shop flavour. I had some rather grim fish and chips recently. I could taste the oil for hours afterwards; I could feel it swilling around inside me. It did not remind me of my roast potatoes.
Some people assert that you should boil potatoes thoroughly before roasting, so that their surfaces rough up and go crispy. I have started to think that cooking potatoes twice, and thus expelling most of their nutrients and a good deal of their flavour, is going too far to achieve this crispiness. However, I do think that it is worth getting rid of some of the surface starch of maincrop potatoes such as King Edward and Maris Piper, which otherwise acquire tough and slimy exteriors in the oven.
I cut up the potatoes, put them into cold water, and bring them to the boil. I simmer them for about three minutes, drain them, and return them to the pan, stirring them on a low heat to dry them out. As soon as they start to stick to the pan I turn off the heat, and let the potatoes carry on steaming for a minute or two.
I do not pre-boil new potatoes for roasting. The drawback is that their surface starch can cause them to stick to the roasting pan.
I pour enough sunflower oil into the roasting pan to give a generous surface layer, and put the pan into a gas mark 6/200 C oven at the same time as I turn on the heat under the potatoes. When the potatoes are dry, I take out the roasting pan, put it on the hob with a low to medium heat under it, and pour in the potatoes. They should sizzle fiercely. I turn them in the oil, and put them back in the oven.
Timings vary, depending on how many potatoes you've got (they should sit in a single, uncrowded layer) and on whether there is anything else in the oven. I usually look at them after 20 minutes, turning them if the undersides are brown. In a hot oven (7/220 C, say), you can roast potatoes in half an hour. I usually give them 45 to 60 minutes.
How big should they be? "No bigger than half an egg," Xanthe Clay instructs. I confess that I sometimes cut them smaller than that. They're more crunch than potato: more sunflower oil than starch. But very tasty.