They say the Belgians make the very best pomme frites and this version here is based on the double frying technique that they generally employ.
1 large potato per person
A neutral oil for deep frying
To make the frites peel and chop into thick or thin (as you prefer) chips/fries and put into large bowl filled with cold water. The Belgian way is for very thin frites and if you have a good mandolin it will probably have a setting on it to slice the potatoes very quickly.
In a deep wok or pot heat about 1 litre of oil (I usually use a neutral oil like sunflower, but groundnut would also be okay....it needs to have a high smoking point) to about 150C. On my cooker that is a medium heat. Make sure the oil is hot, drain the potatoes, dry on a clean dish cloth and add the potatoes to the oil. The oil will splutter and hiss quite vigorously at this stage so stand back.
Cook potatoes for about 5 mins, remove and drain.
Just as you are about ready to eat, heat the oil to 185C (medium-hot setting) and again when hot put the partly cooked frites back in again. Give them another 5 mins, (maybe less, keep an eye on them) remove, drain on kitchen paper, put in a dish and give them a really good grind of sea salt.