Place potatoes in a large saucepan and cover with cold salted water. Bring to a boil and simmer for 15 minutes or until fork-tender.

Drain the potatoes and allow them to sit in the colander for 2 to 3 minutes to steam-dry.

Preheat the air fryer to 400°F (200°C).

On a flat work surface, use the bottom of a heavy glass or measuring cup to gently press each potato down until it is approximately 1/2-inch thick.

In a large mixing bowl, combine the smashed potatoes with olive oil, salt, pepper, garlic powder, and rosemary. Toss gently to ensure even coating without breaking the potatoes apart.

Arrange the potatoes in a single layer in the air fryer basket, ensuring they do not overlap to allow for optimal airflow.

Air fry for 15 to 20 minutes, flipping once at the 10-minute mark, until the edges are golden brown and crispy.

Remove from the air fryer and serve immediately while the internal temperature remains high.