Preheat oven to 180°C, 160°C fan forced. Line the base and sides of a 12 cm x 22 cm loaf pan with baking paper.
Place the bananas in a large bowl and mash with a fork until mostly smooth. Add the eggs, buttermilk, and oil and whisk to combine. Add the caster sugar, brown sugar, and vanilla extract and mix well.
Sift in the flour, bi carb soda, and salt. Fold gently with a spatula until combined. If using add ins such as choc chips, coconut, or nuts, fold them through now.
Pour the batter into the prepared loaf pan. If using the extra banana, place it on top. Bake for 1 hour 10 minutes to 1 hour 15 minutes, or until a skewer inserted into the centre comes out clean. Start checking at the 1 hour 5 minute mark.
Remove from the oven and drizzle the honey or golden syrup over the top. Use a pastry brush to coat the surface. Cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing.