1) Preheat the oven to 220C/Gas 8.
2) Cut the potatoes lengthwise into 1/2 cm-thick matchsticks and toss with the oil and 1/2 teaspoon salt.
3) Spray a baking sheet with cooking spray. Arrange the potatoes in a single layer on the baking sheet and bake until the fries are tender and crisp, about 30 minutes.
Season with additional salt, to taste. Serve immediately.