01 - Preheat air fryer to 320°F for 5 minutes to ensure proper baking temperature.
02 - Grease and line a 7-inch round cake pan that fits comfortably inside your air fryer basket.
03 - Whisk together flour, sugar, cocoa powder, baking soda, and salt in a large bowl until evenly incorporated.
04 - Combine Guinness, buttermilk, melted butter, eggs, and vanilla extract in a separate bowl. Whisk until smooth and well blended.
05 - Pour wet ingredients into dry ingredients. Stir gently until just combined, being careful not to overmix.
06 - Pour batter into prepared cake pan and smooth the top with a spatula for even baking.
07 - Place pan in preheated air fryer basket. Cook for 23 to 27 minutes until a toothpick inserted in the center comes out with a few moist crumbs.
08 - Remove cake from air fryer and let cool in pan for 10 minutes. Transfer to wire rack to cool completely.
09 - Dust with powdered sugar before serving. Optionally top with whipped cream or chocolate ganache.