Preheat the oven to 350F. Grease a 9x5" loaf pan and set it aside.
In a medium bowl, whisk together the flour, baking powder, salt and baking soda. Set it aside.
In a large bowl, using a hand mixer, beat the butter until it is creamy, about 1 minute. Then beat in the sugar until it's nice and fluffy.
Add the eggs, mashed banana, buttermilk and vanilla extract. Beat until combined.
Next, add the dry ingredients to the wet and mix until just combined.
Pour the batter into the prepared loaf pan. Bake for 50-55 minutes, or until a toothpick comes out clean from the center.
Place the pan on a cooling rack. After about 15 minutes, gently run a knife around the edges to loosen the bread. Carefully remove it from the pan.
Let it cool out of the pan on the wire rack. Once it's cool, slice and serve. Store any leftovers in an airtight container.
For buttermilk banana muffins, fill greased muffin tins about 2/3 of the way full and bake @ 350F for 18-20 minutes, or until a toothpick inserted into the center of the muffins comes out clean.
