Method

Peel the potatoes and cut into slices about 7mm thick
Boil the potatoes in salted water for 5-10 minutes, then drain.
The cooking time will depend on the potatoes. Floury ones won't need as long
Cut the onion in half and then slice it into semi circles
Heat some Olive Oil in a wok or large frying pan and sauté the potatoes, turning to ensure evenly cooked
Transfer the potatoes to an oven dish
Fry the onions gently until softened
Add the onions to the potatoes and mix together
Bake for 15-20 minutes in pre-heated oven 170c