For frying potatoes, use a firm to extra-firm potato such as Nicola, Charlotte, Belle de Fontenay, Gourmandine, Jazzy, Annabelle and Marilyn.
Cook firm potatoes in water without salt until almost done. Allow them to steam dry and cut them into generous slices. In a heavy frying pan, heat a good-sized pat of butter and fry the slices over medium heat, continually turning until golden brown. Then add some finely chopped onion and some salt and continue to fry and turn until the crusts are brown. If the pan gets too dry, add some butter.
Tip: A trick to make it look like potatoes have been fried is to add paprika powder to some grease in the pan and to stir slices of potatoes around in it. You don't really fry them, which can save you a fair amount of time.