Step 1: Preheat your oven to 350°F (175°C) and grease a 9×5 inch loaf pan thoroughly.
Step 2: In a large mixing bowl, mash the overripe bananas using a fork or whisk until mostly smooth.
Step 3: Stir the melted butter into the mashed bananas until well combined.
Step 4: Mix in the sugar, beaten egg, and vanilla extract. Whisk until the mixture is pale and slightly frothy.
Step 5: Sprinkle the baking soda and salt over the wet mixture and stir gently.
Step 6: Fold in the flour using a spatula, being careful not to over-mix. Stop as soon as no dry flour streaks remain.
Step 7: If using macadamia nuts, gently fold them in at this stage.
Step 8: Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Step 9: Bake for 55 to 65 minutes, or until a tester comes out clean from the center of the loaf.
Step 10: Allow the bread to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.