In a medium saucepan, add two bananas and cook them on a low heat, mashing the mixture together.

To a medium bowl, add the sugar, oil, egg, sourdough starter, baking powder and vanilla extract. Fold in the flour then add the banana mixture.

Line a 900g loaf tin with baking parchment, then pour in your mixture and cover with cling film.

Leave for 6 hours. This will help your batter rise and for it to develop its tangy sourdough flavour.

Preheat your oven to 180°C / 350°F.

Cut your remaining banana in half, then dip one half in brown sugar on both sides (the other half is for you to eat whilst you wait).

Uncover your loaf mixture, drop the sugar-dipped half banana on top, and bake for 60 minutes.

Your cake's ready when you drop a fork into the cake and none of the mixture sticks to it. Leave to cool then dig in!