Cut each potato lengthwise into 3/8-inch-thick slices, then slice sections into 3/8-inch-wide sticks.
Place potatoes in a bowl of cold water. Let soak to release excess starches, about 5 minutes; drain. Pour boiling water over the potatoes until they’re covered by a few inches. Let sit for 10 minutes.
Drain potatoes and transfer onto some paper towels. Blot off excess water and let cool completely, at least 10 minutes.
Place cooled potatoes in a mixing bowl. Drizzle with oil and season with cayenne; toss to coat.
Preheat an air fryer to 375 degrees F (190 degrees C).
Stack potatoes in a double layer in the fryer basket. Cook for 15 minutes. Slide basket out and toss fries. Continue frying until golden brown, about 10 minutes more.
Toss fries with salt in a mixing bowl. Serve immediately.
