Preheat an oven to 180 C / Gas 4. Grease a 900g loaf tin.
In a mixing bowl, beat the butter and sugar together with an electric mixer until thoroughly blended. Beat in the eggs, one at a time, and add the bananas, bicarbonate of soda, baking powder, salt and vanilla extract. Stir in the flour by hand until barely combined, and gently fold the macadamia nuts into the batter.
Pour the batter into the prepared tin, and bake on the oven's middle shelf until a skewer inserted in the middle of the loaf comes out clean, 60 to 65 minutes.
Remove from oven, and let the loaf rest for 10 minutes before turning out from the tin.