In a large bowl, beat butter into coffee until butter is melted.
Beat in egg and vanilla until combined
In a separate bowl, whisk together flour, sugar, cocoa powder, baking powder, baking soda, and salt.
Add dry ingredients to wet and beat until combined
Preheat air fryer to 350°F, about 3-4 minutes
Line a square cake pan with parchment paper or spray with cooking spray
Pour batter into prepared cake pan
Bake in the air fryer for 20 minutes or until a toothpick inserted in center comes out clean
Cool in pan. Frost once cooled if desired.
Store covered at room temperature for up to three days
