Preheat your air fryer to 380°F and lightly grease a 6-inch round cake pan or 8x8 inch baking dish that fits your air fryer basket. While the air fryer heats, gather all ingredients and ensure your egg and butter are at room temperature—this helps them emulsify properly with the other ingredients for a tender crumb. Room temperature ingredients mix more smoothly and create a better texture in the finished brownies.

In a medium bowl, whisk together the sugar, cocoa powder, flour, salt, baking powder, and espresso powder. I always sift the cocoa powder first to remove any lumps and ensure even distribution of color and flavor throughout the brownies. Whisking these dry ingredients together for about 30 seconds ensures the leavening agents and salt are evenly distributed, which gives you consistent results.

In a separate small bowl, whisk together the melted butter (cooled to room temperature), egg, and vanilla until well combined and slightly thickened, about 30 seconds. Pour the wet mixture into the dry ingredients and stir gently with a spatula just until combined—don't overmix, as this can lead to tough brownies. A few small streaks of flour are fine; stop stirring as soon you don't see dry ingredients at the bottom of the bowl.

Pour the batter from Step 3 into your greased pan and smooth the top with a spatula. Place the pan in the preheated air fryer basket and air fry at 380°F for 15 minutes. The brownies are done when a toothpick inserted in the center comes out with just a few moist crumbs clinging to it—they'll continue to cook slightly as they cool, so don't overbake.

Remove the pan from the air fryer and let the brownies cool in the pan for 5-10 minutes before slicing. I find that letting them cool slightly makes them easier to cut cleanly and helps them set up properly. Serve warm or at room temperature with ice cream, whipped cream, or enjoy them on their own.