Add the bananas, sugar, oil, cinnamon and salt to the bowl of the food processor. Blitz until smooth. Add the sourdough starter, flour and bicarbonate of soda (baking soda) and blitz until just combined. Scrape down the sides of the food processor to make sure everything is incorporated
220-240 g overripe bananas (peeled weight), 150 g (3/4 cup) light brown sugar, granulated sugar or caster sugar, 90 g (1/3 cup + 2 tsp) neutral oil or light olive oil, 1 tsp ground cinnamon, 1/4 tsp fine table salt, 150 g (3/4 cup) sourdough starter/discard, 120 g (1 cup) plain white flour, 1 tsp bicarbonate of soda