Add all the ingredients to a bowl and mix well until the cashews are evenly coated.
You can cook the rosemary nuts either in the air fryer or in the oven.
If using an air fryer, line the basket with baking paper and arrange the cashews in a single layer. Cook in two batches if needed to avoid overcrowding, which helps them toast evenly.
Air fry at 180°C (350°F) for 5–8 minutes, shaking the basket halfway through cooking.
If using the oven, spread the cashews on a lined baking tray and bake at 180°C (350°F) for 10–12 minutes, mixing halfway through.
Remove from the air fryer or oven once golden and fragrant, then allow the nuts to cool completely. They will crisp up further as they cool.