Peel the potatoes and then slice them into thin matchstick shapes. If you have a mandolin, this is easy and takes minutes, but please ensure that you use the guard!
Place the sliced potatoes in a large bowl of cold water and allow them to soak for 20 minutes.
If you are using a deep fat fryer, heat the oil to 170°C or 340°F. If you are using a high-sided frying pan, heat 1cm of oil to 170°C or 340°F, but ensure your frying pan is slab-sided and at least 3-4cm deep.
Before you fry, dry the potatoes thoroughly on a clean tea towel.
If you are using a deep-fat fryer, you can fry this amount of potatoes in one go, and they should be cooked until crisp and golden, which will take 4-5 minutes. If you are frying in a pan, then you will need to cook in two batches. Use a slotted spoon to turn over the potatoes in a frying pan every minute or so; again, they will take 4-5 minutes to cook.
Remove the potatoes and place them on kitchen paper to soak up any excess oil. Season them with salt and pepper immediately.