Preheat the oven to 350°F and prepare a loaf pan by greasing with butter or cooking spray.

In the bowl of a stand mixer, cream the butter and the sugar on medium speed.

Once it is light and fluffy, add the eggs one at a time.

Add the vanilla, mashed bananas, and sour cream (or yogurt). Beat until combined.

In a separate bowl, mix together the flour, baking powder, baking soda and salt.

On medium-low speed, incorporate the flour mix into the wet ingredients.

Transfer the batter to the prepared loaf pan.

Bake for 70 minutes or until a toothpick inserted into the center of the loaf comes out clean.