Great roasties don't happen by accident. Parboil the potatoes and get the oven on to heat up your oil. You want it smoking hot.
Once the spuds are parboiled, drain well then give them a shake. Keep the lid on and bash them about. (If you've overcooked them, I'd change the menu to mash.) You want broken up edges – what we call 'ruffled' – these are the bits that will crisp up in the oven and keep the inside deliciously soft.
Put the spuds in the tray, carefully baste them in the hot oil – this seals them and stops them sticking. Spread the potatoes out; don't overcrowd them or put them on top of one another.
Slide them into the oven for 45 minutes or so, turning them over once halfway through. Sprinkle your golden, ruffled roasties with salt. Serve and accept compliments.