- Preheat the oven to 350°F and grease a 9-x-5-inch loaf pan.
- Beat the butter and brown sugar together until smooth. Stir in the banana, then stir in the egg and vanilla. In a separate bowl, stir the all-purpose flour, whole wheat flour, baking soda, cinnamon and salt to combine. Add this to the butter mixture and stir until evenly blended. Add the chocolate chips then scrape the batter into the prepared pan, spread evenly.
- Bake the cake for about an hour, until a tester inserted in the centre of the cake comes out clean. Cool the cake for 30 minutes in the pan, then turn out to cool completely.