1) Heat oven to 240C/Gas 9 and arrange rack in top.
2) Peel potatoes and cut lengthwise into 1.5cm-wide planks. Cut planks lengthwise into 1.5cm-wide strips then cut strips in half crosswise. Cover potatoes in hot tap water and let soak for 10 mins before proceeding.
3) Meanwhile, combine oil and garlic in a small saucepan and bring to a simmer over medium-low heat. As soon as the mixture is aromatic and the garlic makes a sizzling noise, remove it from the heat and set aside to cool.
4) When potatoes are done soaking, drain, and thoroughly pat dry with paper towels. Place potatoes on a baking sheet, drizzle with garlic oil, sprinkle with 1 tsp of the salt, and turn to coat well. Spread chips out evenly across baking sheet and roast until chips are just beginning to colour, about 25 mins. Using a spatula, scrape sheet to turn chips and continue to roast until crisp on outside, potatoes give way when pierced with a knife, and are golden brown, about 15 mins more.
5) Remove chips from oven, season with remaining 1 tsp of salt, and serve immediately.