Heat the oven to 220C/425F/gas mark 7. Bring a large pot of salted water to a boil, then cook the potatoes for nine minutes, until starting to soften at the edges but still holding their shape.
Drain, leave to steam dry for five minutes, then tip into a large bowl. Add the sunflower oil and a tablespoon of salt, toss to coat, then tip out on to two large oven trays lined with greaseproof paper (you’ll need two trays, so the potatoes aren’t overcrowded).
Bake for 40-50 minutes, stirring every now and then, until golden brown and crisp.
While the chips are cooking, heat the olive oil in a small saucepan on a medium-high heat, then gently fry the garlic for three or four minutes, until pale golden brown. Lift out the garlic with a slotted spoon and transfer to a plate; reserve the infused oil.
Once the chips are cooked, sprinkle with the dried garlic, drizzle with the infused olive oil and return to the oven for four minutes to heat through. Remove from the oven and, while the chips are piping hot, sprinkle with feta and oregano. Serve at once.