Preheat oven to 350ºF (175ºC). Prepare an 8″ X 4″ loaf pan.
In a large bowl combine flour, sugar, baking powder, baking soda and salt.
In a separate bowl, beat together egg, meltedbutter and mashed banana. Add to the dry ingredients and stir until just moistened (do no over-mix or loaf will be tough). Gently fold in walnuts.
Pour batter into loaf pan and bake for about 50 minutes, or until golden brown and toothpick inserted in centre comes out clean. Transfer to wire rack to cool at least 30 minutes before slicing.