The answer is an apple. One grated apple in any banana cake is a miracle worker towards boosting the banana taste.
Here is a recipe you could try out if you are feeling skeptical.
285g/1,5 cups* flour
225g/1,25 cups sugar
110g/0,75 cups butter
5g bicarbonate of soda
85ml/0,5 buttermilk, diluted yogurt or milk with squirt of lemon in it
Preheat oven to 180C/350F. Line a loaf tin approx. 23 x 13cm /9 x 5 1/2inches with baking paper.
In a large bowl measure flour, sugar, and soda. Set aside.
Melt butter until almost liquid but not hot. Pour in the milk with squirt of lemon (or the yogurt; or the buttermilk). Beat in the eggs and add them in as well.
Mix dry ingredients with the butter, milk and eggs until well combined in a liquid dough.
Mash bananas with a fork. Grate the apple. Mix in with the dough and pour in the pre-lined tin. Bake in the oven for 45min or until a toothpick inserted in the middle of the loaf comes out clean.
*Cup approx. = 150g