Prepare the Pan:Grease a 6-inch round baking pan and line the base with parchment paper.
Melt Chocolate & Butter:Add chocolate chips and butter to a microwave-safe bowl. Heat in 30-second intervals, stirring between each, until smooth.
Mix the Wet Ingredients:Whisk in sugar, egg, and vanilla until the mixture looks glossy.
Add Dry Ingredients:Sift in flour, cocoa powder, and salt. Fold gently until just combined.Stir in extra chocolate chips or nuts if using.
Air Fry:Pour the batter into the prepared pan and smooth the top.Preheat air fryer to 150°C. Place the pan in the basket and cook for 15 minutes, or until the top is crackly and the center looks soft-but-set.
Cool & Serve:Allow the brownies to cool completely in the pan before removing and slicing.(They will firm up as they cool.)