In a large mixing bowl, cream together the butter and sugar, then add the egg, followed by the banana, sour cream, and vanilla extract, and mix well.
In another mixing bowl, mix the flour and baking soda.
Mix the two mixtures, mix well, so they combine.
Fold in the diced walnuts, and mix again.
Spray your baking pans with olive oil. Pour the batter into the prepared pan, about 2/3 way full.
Set the pan into the air fryer, and set the temperature to 320 degrees F for 20 minutes.
When the time is up, place a toothpick in the pound cake, and check to see that the toothpick comes out clean. If not, add another 5 minutes.
Plate, serve, and enjoy!