Preheat oven to 350°F Lightly grease a 9×5-inch loaf pan.
In a large bowl, whisk together flours, baking powder, baking soda, salt and spices.
In a medium bowl, whisk together brown sugar, banana, molasses, buttermilk and vegetable oil. Pour into dry ingredients and stir until just combined. Pour into prepared pan and sprinkle with coarse sugar, if desired.
Bake for about 45 minutes, until a toothpick inserted into the center of the loaf comes out clean.