Place the butter in a bowl, beat in the sugar and salt. Add the eggs, beat together using the whisk on a hand mixer until the mixture becomes lighter in colour. Mix in the banana, kiwi and buttermilk.
Mix the flour, walnuts, baking powder and sodium bicarbonate, mix into the banana mixture along with the kiwi. Transfer the cake batter to the prepared tin.
Approx. 1 hr. in the centre of an oven preheated to 180°C. Remove from the oven, allow to cool slightly, remove the banana bread from the tin and leave to cool on a rack.