Roast potatoes under the grill
I know - a lot of you lucky people boast the posession of two ovens or more, plus a steam oven plus a microwave. But there are still some unpriviledged folk like me who have a solitary oven which refuses to cook two things at the same time as well. So if your veg or gratin hogs the oven, you're a bit stumped with the spuds.
The cheat's trick is to cook them under the grill. Preboiling is a must, to the point where they are tender enough to eat and nice and crumbly. Then just preheat the desired fat in the grill tray and slide the potatoes in, to crispen them there, only tossing every now and then. The beauty of this approach is that a/ you can present them as roasties, and they taste almost as good as, and b/ that you can surreptitiously throw another batch in while people are busy devouring the first.