Preheat oven to 350° F. Grease a 9 x 5 inch loaf pan or muffin tin with cooking spray.
Peel bananas, add to mixing bowl and mash to desired consistency. Add in softened butter and egg and mash together.
Add in all dry ingredients and stir until just combined.
Pour batter into loaf pan and place in the oven. Bake for 40 - 50 minutes until toothpick inserted in centre comes out clean. Remove from oven and cool for 10 minutes before turning out onto cooling rack.
If you are making muffins, fill each muffin cup ¾ full. Bake for 18 to 21 minutes until they spring back when touched. Remove from oven and cool for 10 minutes before turning out onto cooling rack.