Prep your pan and air fryer. Line a 7- or 8-inch square pan (or a round cake pan that fits in your air fryer basket) with parchment, leaving overhang for easy lifting. Lightly spray the sides. Preheat the air fryer to 320°F (160°C) for 3–5 minutes.

Melt chocolate and butter. In a microwave-safe bowl, melt the dark chocolate and butter in 20–30 second bursts, stirring between each, until smooth. Stir in the oil. Let cool for 2 minutes so it’s warm, not hot.

Whisk in sugars. Add the granulated and brown sugar to the chocolate mixture and whisk until glossy and thick, about 30 seconds.

Add eggs and vanilla. Whisk in the eggs one at a time until the batter looks shiny and slightly thickened. Stir in the vanilla. Don’t overmix, but make sure there are no streaks of egg.

Combine dry ingredients. In a separate bowl, whisk the flour, cocoa powder, fine sea salt, and espresso powder (if using).

Fold to finish the batter. Use a spatula to gently fold the dry mixture into the wet until just combined. The batter will be thick and glossy. Avoid overmixing to keep the brownies tender.

Pan and smooth. Scrape the batter into the prepared pan and smooth the top evenly. For a crackly top, let the batter sit 3–5 minutes before baking.

Air fry. Place the pan in the basket and bake at 320°F (160°C) for 20–24 minutes, rotating the pan halfway if your air fryer has hot spots. Start checking at 18 minutes.

Check doneness. The center should be set but still soft. A toothpick inserted 1 inch from the edge should come out with a few moist crumbs; the center may have a slight jiggle. If it looks wet, air fry in 2–3 minute increments.

Cool completely. Remove the pan and let brownies cool in the pan on a rack for at least 45–60 minutes. For the cleanest slices, chill 20 minutes after cooling.

Finish and serve. Lift out using the parchment. Sprinkle with flaky sea salt if you like. Cut into 9 generous or 16 smaller squares. Serve as is or warm slightly and top with vanilla ice cream.