Preheat oven to 180°C. Combine the flour, bran, bicarbonate of soda, spice, sugar and molasses in a large bowl and mix well. Whisk the sour cream, olive oil, eggs and mashed banana in a second bowl.
Add the banana mixture to the flour mixture and stir to combine, then spoon into a lined medium loaf pan. Place the slice banana on top, then bake for 40-45 minutes, until a skewer can be inserted and removed cleanly. Turn out, then cook on a wire rack.