Grease a small Bundt cake pan with cooking spray.
In a bowl, add the butter and sugar and whisk until light and creamy.
Add the egg and whisk until smooth and fluffy.
Now add the flour, and salt and alternately with milk and mix well.
Place mixture into the prepared cake pan evenly.
Slide the Air Fryer Basket inside and adjust the temperature to 350 °F to preheat for 5 minutes.
After preheating, arrange the cake pan into the Air Fryer Basket.
Slide the basket into Air Fryer and set the time for 15 minutes or until a toothpick inserted into the center comes out clean.
After cooking time is finished, remove the cake pan from Air Fryer and place onto a wire rack to cool for about 10 minutes.
Carefully invert the cake onto the wire rack to completely cool before slicing.
Dust the cake with icing sugar and cut into desired size slices.