Preheat your air fryer to 350°F (175°C) and thoroughly grease and flour a bundt pan.

In a medium bowl, whisk together the flour, baking powder, and salt; set aside.

In a large bowl, beat the softened butter and granulated sugar together until light and fluffy (about 4 minutes).

Add the eggs one at a time, mixing well after each addition, then stir in the sour cream and vanilla extract until smooth.

Gradually add the flour mixture and milk, alternating between the two, mix until just combined.

In a small bowl, combine brown sugar and cinnamon.

Pour half of the batter into the prepared bundt pan, sprinkle half of the cinnamon-sugar mixture over it, then layer the remaining batter on top.

Use a knife to swirl the batter gently for a ribbon effect.

Bake in the preheated air fryer for 50-60 minutes or until a toothpick comes out clean.

Let it cool in the pan for 15 minutes before inverting onto a wire rack to cool completely.

Whisk together the powdered sugar, milk, and vanilla until smooth, then drizzle over the cooled cake.