Preheat your oven to 170°C fan / 190°C conventional / 375°F. Grease your loaf tin and line it with parchment for easy release.
Peel and mash the bananas in a large bowl using a fork until mostly smooth. A few lumps are fine - they add texture.
Add the eggs, melted butter, vanilla, and sugar to the mashed bananas. Whisk together until fully combined.
In another bowl, mix the flour, baking powder, bicarbonate of soda, cinnamon, and salt. Sift if your flour is lumpy.
Gently fold the dry ingredients into the wet mixture until just combined - don't overmix, as it can toughen the loaf. Fold in any extras like nuts or chocolate chips at this stage.
Pour the batter into your prepared tin and smooth the top. Bake for 50-60 minutes, or until a skewer comes out clean from the centre.
Let the banana loaf cool in the tin for 10-15 minutes, then transfer it to a wire rack. Wait until fully cooled before slicing.