Preheat your oven to 375°F (190°C). Grease a muffin tin or line with paper liners.
In a large bowl, mix wheat bran and buttermilk. Let it sit for 10 minutes.
In another bowl, whisk together oil, egg, brown sugar, and vanilla extract.
Add the wet ingredients to the bran mixture and stir until combined.
In a separate bowl, combine flour, baking soda, baking powder, and salt. Add to the bran mixture and stir until just combined.
Fold in the raisins.
Spoon the batter into the prepared muffin tin, filling each cup about ⅔ full.
Bake for 15-20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Let the muffins cool in the tin for a few minutes, then transfer to a wire rack to cool completely.