Lightly grease a small heat-safe pan that fits in your air fryer with cooking spray. Set aside. 

In a microwave-safe bowl, melt chocolate chips and butter in 30-second 50% power increments, stirring occasionally until smooth.

Whisk in the cocoa powder and set aside to cool.

Preheat the air fryer to 330 degrees F while you make the batter.

In a separate bowl, whisk together sugar, egg, and vanilla until well combined.

Add warm chocolate mixture and whisk well.

Add flour and salt and fold in with a spatula until just combined.

Sprinkle the top with additional chocolate chips, if desired.

Pour batter into the prepared pan and place it in the air fryer basket.

Air fry for 22-25 minutes, until a toothpick inserted in the outer edges comes out with dry crumbs. The center will still be a little gooey, but the brownies will continue to cook in the middle after removing.