Preheat Oven: Preheat your oven to 180°C (160°C fan) or Gas Mark 4. Grease a 2lb loaf tin and line it with baking paper.
Mash the Bananas: In a large bowl, mash the bananas with a fork until smooth.
Mix Wet Ingredients: Add the melted butter, caster sugar, beaten egg, and vanilla extract to the mashed bananas. Stir until combined.
Combine Dry Ingredients: In a separate bowl, mix the plain flour, bicarbonate of soda, and salt. If using cinnamon, add it here.
Combine Wet and Dry: Gradually fold the dry ingredients into the wet mixture until just combined. Do not overmix.
Add Extras: If adding nuts or chocolate chips, gently fold them in now.
Bake: Pour the batter into the prepared loaf tin and smooth the top. Bake for 50-60 minutes, or until a skewer inserted into the center comes out clean.
Cool and Serve: Let the banana bread cool in the tin for about 10 minutes, then transfer to a wire rack to cool completely.