1. Peel and cut the potatoes into 6mm fries using a serrated knife. Keep the cut fries in a bowl of water to stop them from browning. Once they are all cut, drain in a colander.

2. Transfer potatoes into a large pot with vinegar and salt. Cover with 2 litres of cold water. Bring to a boil and then simmer for 5 minutes, until they are just cooked. Start checking at the 4 minute mark – if they overcook, they will break. Drain and spread on paper towels over 2 trays. Allow to dry for 5 minutes.

3. Meanwhile, fill a deep, heavy-based pot with 4cm of oil, ensuring there is at least 5cm above the oil to the rim (there is risk of hot oil boiling over). Heat the oil to 205C over high heat. Separate the potatoes into 3 piles, to cook them in 3 batches.

4. Carefully place a small handful of fries from the first batch in the oil – the oil will bubble up. Wait until the bubbles subside (about 5 seconds) before continuing with the rest of the first batch. The oil temperature will drop to about 180C. Cook fries for 50 seconds, agitating occasionally with a spider strainer, then remove and drain on paper towels on a tray, spreading them out so they are not stacked on top of each other. Repeat with remaining fries, allowing the oil to return to 205C after each addition.

4. Cool cooked fries for 30 minutes. At this stage, they can be frozen up to 2 months for fries on demand!

5. Heat the same oil to 205C over high heat. Place half the potatoes into the oil (don't worry, it won't bubble up this time) and fry for 3 minutes, adjusting the heat to maintain a temperature of 180C. Drain in a bowl lined with paper towels. Repeat with remaining fries. Taste and season with salt, if required.

Note: The first batch of cooked fries will stay hot and crisp for the 3 minutes it takes to cook the second batch, but if you want to make sure, you can put them on a wire rack set on a sheet tray in a 90C oven while the second batch cooks.

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