Preheat oven to 170°C, grease and line a loaf pan.
Cream the butter and sugar until fluffy. Add eggs one at a time, mixing well. Stir in vanilla.
Mix in mashed bananas.
Alternately fold the dry ingredients and buttermilk into the banana mixture until just combined.
Pour batter into the pan and bake for 50-60 minutes, or until a toothpick comes out clean.
Let cool, then slice and enjoy!