Preheat oven to 350 degrees. Prepare a 9x5 loaf pan with butter or shortening and flour. Tap to remove excess flour.

In a mixing bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.

In a separate mixing bowl, cream the butter and sugar until light and fluffy. Add the eggs, vanilla extract, and sour cream. Mix in bananas alternating with flour mixture until combined.

Stir in nuts if desired.

Place in the oven and bake for 60 minutes or until a toothpick inserted in the center comes out clean. If the top begins to darken too much, tent with aluminum foil.

Cool for 5 to 10 minutes in the pan before removing to a wire rack to cool completely.