1) Preheat the oven to 230C/Gas 8. Spray a baking tray with cooking spray.
2) Cut each of the potatoes in half lengthwise. Rest each half on its flat side and cut each half lengthwise, straight down into 4 even slices; you will have 16 slices altogether. Cut the rounded edge off the outermost slices so each slice can lay completely flat on either side. Put the potatoes into a medium bowl and toss with the oil.
3) Place the potatoes on a baking tray and bake for 20 minutes. Sprinkle the potatoes with cheese on their upward-facing side and continue to bake for another 15 to 20 minutes, until crisp and golden brown. There is no need to turn them.