In a medium bowl, whisk together the flour, cocoa powder, baking powder, espresso powder, and salt. Sifting the cocoa and baking powder beforehand removes lumps and ensures even distribution of the leavening agent throughout the batter, which is crucial for consistent texture in brownies. Set this dry mixture aside.

In a separate bowl, whisk together the melted and cooled butter, eggs, vegetable oil, and vanilla extract until well combined. Add the sugar and whisk until the mixture is slightly thickened and well incorporated. This emulsification helps create a fudgy texture. Pour the dry ingredient mixture from Step 1 into the wet ingredients and fold together gently with a spatula until just combined—do not overmix, as this keeps the brownies tender rather than cake-like.

Preheat your air fryer to 330°F for about 5 minutes. While it heats, lightly grease a 7-inch round or 6x6 inch square baking pan (or similar size that fits in your air fryer basket) with butter. I prefer this lower temperature for air fryer brownies because it allows the center to cook through without the edges overbaking.

Pour the batter from Step 2 into the prepared pan and spread it evenly. Carefully place the pan in the preheated air fryer basket and air fry at 330°F for 15 minutes. The brownies should be set around the edges but still slightly jiggly in the very center when done—this is intentional, as they will continue to cook slightly as they cool and will set up to the perfect fudgy consistency.

Remove the pan from the air fryer and let the brownies cool in the pan for at least 15-20 minutes before cutting into squares. This resting time allows the structure to set properly so they hold their shape cleanly when you cut them. For extra fudgy brownies, I recommend serving them while still slightly warm.