Preheat the oven to 350°F (175°C). Grease a loaf pan or line it with parchment paper for easy removal.
Mash the bananas in a large mixing bowl until smooth. Add the melted butter and stir until well combined.
Add sugar, egg, and vanilla to the banana mixture. Stir until the ingredients are fully incorporated.
Gently fold in the self-rising flour. If you like, add cinnamon and chopped nuts to the mixture for extra flavor and texture. Stir just until combined – be careful not to overmix.
Pour the batter into the prepared loaf pan and spread it evenly.
Bake for 55-65 minutes, or until a toothpick inserted into the center comes out clean.
Cool the banana bread in the pan for 10 minutes, then transfer it to a wire rack to cool completely before slicing.