Preheat the oven to 350 degrees F.
Spray an 8 ½ by 4 ½ inch loaf pan with cooking spray.
In a mixing bowl, combine the flour, bran. baking powder, baking soda, and cinnamon and stir until very well mixed.
Add the raisins and mix again.
In another bowl, whisk together the buttermilk, egg, and vanilla.
Pour the liquid ingredients into the dry ingredients and stir until fully blended.
Transfer the mixture to the prepared loaf pan. If using nuts, sprinkle them across the top.
Bake for 45 to 50 minutes, or until a knife inserted in the center comes out clean. Place the bread, while still in the pan, on its side on a wire rack to cool.