01 - Preheat air fryer to 320°F for 5 minutes to ensure even baking temperature.
02 - Grease and line a 7-inch round cake pan that fits comfortably in your air fryer basket to prevent sticking.
03 - In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, and salt until thoroughly blended.
04 - In a separate bowl, combine Guinness, buttermilk, melted butter, eggs, and vanilla extract. Whisk until smooth and fully incorporated.
05 - Pour wet ingredients into dry ingredients and stir until just combined. Avoid overmixing to prevent dense texture.
06 - Pour batter into prepared cake pan and smooth the top evenly with a spatula.
07 - Place pan in preheated air fryer basket and cook for 23 to 27 minutes, until a toothpick inserted in center comes out with a few moist crumbs.
08 - Remove cake from air fryer and let cool in pan for 10 minutes, then transfer to wire rack to cool completely.
09 - Dust with powdered sugar before serving, or top with whipped cream or chocolate ganache if desired.