Preheat the oven to 375 degrees F (190 degrees C). Grease 12 muffin cups or line with paper muffin liners.
Mix together wheat bran and buttermilk in a large bowl; let stand for 10 minutes.
Beat together brown sugar, oil, egg, and vanilla in a separate bowl and add to buttermilk mixture.
Sift together flour, baking soda, baking powder, and salt. Stir flour mixture into buttermilk mixture until just blended. Fold in raisins and spoon batter into the prepared muffin pan.
Bake muffins for 15 to 20 minutes or until a toothpick inserted into the center of a muffin comes out clean. Cool and enjoy!