Melt the unsalted butter in a microwave-safe bowl or on the stovetop. Let it cool for a minute.
In a mixing bowl, whisk together the melted butter and sugar until smooth. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Sift together the flour, cocoa powder, salt, and baking powder in a separate bowl to avoid lumps. Add the dry ingredients to the wet mixture and stir until just combined. Add milk to achieve a smooth batter.
Preheat the air fryer to 325°F (160°C) for 3-5 minutes. Grease a small baking dish or line it with parchment paper. Pour the batter into the dish.
Place the dish in the preheated air fryer and cook at 325°F (160°C) for 15-20 minutes. Check for doneness with a toothpick; if it comes out with a few moist crumbs, it’s ready!
Allow the brownies to cool in the dish for 10 minutes before slicing them into squares. Serve and enjoy!
Notes
If you want to mix it up, try adding chocolate chips, nuts, or peanut butter swirls to your brownie batter for extra flavor!