Preheat oven to 350. Grease and flour a 9x5" loaf pan.
Add butter and sugar to the bowl of a stand mixer and cream together.
Add eggs and sour cream, mixing well to combine and scraping down the sides of the bowl as needed.
In a separate bowl, combine flour, baking powder, salt, and baking soda.
Alternate adding mashed bananas and flour mixture, beginning and ending with flour mixture (⅓ of flour mixture, ½ of mashed bananas, ⅓ of flour mixture, remaining bananas, remaining ⅓ of flour mixture).
Pour batter into prepared pan.
Bake for 50-55 minutes, or until a toothpick inserted in the center comes out clean.
