The very best roasties are made with floury potatoes, although all-rounders are fine. There are two methods: the long way round, boiling first, gives the crispiest, crunchiest results; the second option, cutting them into wedges and roasting from raw, is also pretty good and a bit simpler.
To boil first, heat the oven to 210°C/Gas 7 and put in a baking tray with a thin layer of light olive or sunflower oil or duck or goose fat. Halve peeled potatoes and place them in cold, well-salted water. Bring to the boil, then simmer for a further 10 minutes, until almost cooked through. Drain, leave to dry for a few minutes, then toss them in the colander to roughen their surfaces. Carefully add the potatoes to the preheated baking tray, turning to coat in fat, then immediately return to the oven and roast for 30–40 minutes, until cooked through and golden. Turn them over once or twice during roasting for even results. For variations, see Roast Potatoes with Lemon, Rosemary and Thyme.