In a large mixing bowl, cream together the 1/2 cup butter and 1 1/2 cups granulated sugar then add t3 large eggs, followed by the 1 medium banana, 1/2 cup sour cream, and 1 teaspoon vanilla extract, and mix well.
In another mixing bowl, mix the 1 1/2 cups all-purpose flour and 1 teaspoon baking soda.
Mix the two mixtures, mix well, so they combine.
Fold in the diced 1/2 cup 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 air fryer temperature to 320 degrees F set cook time for 15-20 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.