Preheat your oven to 350 degrees F (180 degrees C), line a large, rimmed baking tray with parchment paper, and lightly grease with some of the olive oil.
Wash the potatoes to remove any dirt (leave as much skin on them as poss.). Halve the potatoes lengthways and place into a medium pot of cold water, add the salt and bring to a boil. Cook for 6-8 minutes to parboil the potatoes.
Drain the potatoes and leave in the colander for 5 minutes so they can dry off.
Slice each potato-half lengthways into 4 wedges. Place into a large bowl, sprinkle over the cornstarch and toss with your hands to coat (see notes).