Preheat oven to 180 degrees Celcius.
Mix the milk and balsamic vinegar and leave for five minutes to curdle.
Combine the flour, baking soda, baking powder and salt in a bowl.
Beat oil and sugar with a hand-held mixer for two minutes.
Add the milk mixture and beat until just mixed. Add the bananas and beat until smooth.
Gradually add flour to the mix, beating in after each addition until mixture is smooth. Do not over-beat.
Line a 23cm square pan with baking paper and brush with oil.
Pour in the batter and bake in the oven for 25 to 30 minutes.
Optional: Ice or dust with icing sugar once your cake has cooled completely.