Preheat the oven to 180C/356F. Grease and line a 20cm (7.8 inch) cake tin.
In a large mixing bowl, combine the flours, baking powder, baking soda and salt.
In a medium mixing bowl, combine the banana, sugar, milk and oil.
Whisk the wet ingredients into the dry, then add the vinegar and vanilla bean paste if you’re using it. Whisk again to combine.
Pour the batter into the lined cake tin and bake for 25-30 minutes or until golden brown and cooked through. If you like a JUST slightly unbaked banana cake, take it out now. Otherwise, cook the cake for an additional 5 or so minutes. Lightly tent the cake with foil if it is taking on too much colour.
Remove from the oven and allow to cool for 10 minutes before removing the cake from the tin and placing on a wire rack to cool completely before icing.