Preheat the oven to 350°F. Grease a 9x5-inch loaf pan or line it with parchment paper.

In a medium bowl, sift together flour, baking powder, baking soda, and salt.

In a large bowl, cream together the softened butter and sugar until light and fluffy.

Add the egg and vanilla extract to the creamed mixture and beat until well combined.

Stir in mashed bananas until evenly incorporated.

Alternately add the dry ingredients and buttermilk to the banana mixture, beginning and ending with dry ingredients. Mix just until combined.

Pour batter into prepared loaf pan, smooth the top with a spatula.

Bake for 55 minutes or until a toothpick inserted into the center comes out clean.

Let the bread cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.