Carefully slice them into thin strips using a sharp knife or a chip cutter.
Place the cut chips into a large bowl and allow to soak for at least an hour. (This pulls out the starch in the potatoes and prevents them from sticking).
Drain the water when ready to cook.
Transfer the chips onto kitchen paper of a large kitchen towel and thoroughly dry them.
Using a deep saucepan
Add a few inches of vegetable oil to a deep saucepan over a high heat until it reaches 150C.
Cook the chips in batches in the oil until the are soft. Will be about 4-5 minutes per batch. You are just starting to cook them at this stage.
Transfer each cooked batch onto paper towel to drain excess fat.
Once all of the chips have been cooked once, turn the heat up on the oil until it reaches 200C.
Once the oil has reached that temperature start to fry the batches again.
Cook the batches until golden brown and crisp.
When cooked remove from the oil and drain on paper towels.
Sprinkle with salt and serve immediately.
Using Deep Fat Fryer
Similar to above except you should be able to cook them in fewer batches possibly in one go.
Once cooked at 150C remove and turn up to 200C and repeat the process.