You have to start with the right type of potato, or you may end up with roast mashed potato! Parboiling reduces cooking time, (I give them about 6 mins in the microwave), after which I make a few slices about half the way through each piece. Then I add a little oil to the bowl and stir the potatoes gently to coat. Salt, pepper and Aromat are next, and maybe a little garlic, too. (We get a garlic bread seasoning in Australia that works really well) Next either put them in with the roast, or wait until the roast is done and while the meat is resting, roast the potatoes. (They probably need a higher heat than you would do the roast at so I do the latter method) Keep an eye on them, but 3/4 hours should be about right.