Mix wheat bran and buttermilk in a large bowl and let soak for 10 minutes
Preheat oven to 375°F (190°C) and line or grease a muffin tin
Add brown sugar, honey or molasses, oil, egg, and vanilla to the soaked bran and stir until smooth
In a separate bowl, whisk flour, baking soda, baking powder, salt, and cinnamon
Fold dry ingredients into wet mixture just until combined
Fold in raisins or nuts if using
Divide batter evenly into muffin cups, filling about ¾ full
Bake for 18–22 minutes until tops spring back and a toothpick comes out clean
Cool 5 minutes in the pan, then transfer to a wire rack