Preheat & Prep: Heat your oven to 375°F (190°C). Line a standard 12-cup muffin tin with paper liners or grease generously with non-stick spray.
Soak the Bran: In a large bowl, combine the wheat bran and buttermilk. Let it sit for 5–10 minutes. This crucial step hydrates the bran and guarantees a tender crumb.
Mix Wet Ingredients: Whisk the egg, oil, brown sugar, and vanilla extract directly into the soaked bran mixture until smooth.
Add Dry Ingredients: Whisk together the all-purpose flour, baking powder, baking soda, cinnamon, and salt in a separate small bowl. Fold the dry mixture into the wet ingredients using a spatula just until combined (do not overmix). Gently fold in raisins or nuts if using.
Bake: Divide the batter evenly among the 12 muffin cups. Bake for 18 to 20 minutes, or until a toothpick inserted into the centre comes out clean.
Cool: Allow the muffins to cool in the pan for 5 minutes before transferring them to a wire rack to cool completely.