Half fill a deep, heavy-based pan with vegetable oil and heat on a medium-to-high heat. Use a mandolin or food chopper to ‘julienne’ the potatoes (no need to peel). Place the julienne potatoes on some kitchen roll and pat to remove excess water.
Place one of the fries in the oil, if it sizzles and rises to the top within a few seconds, the oil is ready. Carefully add on-third of the fries to the pan (it will bubble quite a lot, so it’s best to cook in batches). Fry for 2-3 minutes until golden brown. Use some metal tongs to break any clumps up if the fries stick together. Remove the fries and place on kitchen towels whilst you cook the remaining two batches.