Preheat oven to 375°F. Line a 12-cup muffin tin or lightly grease it.
Soak the wheat bran in buttermilk in a bowl; let stand 10 minutes to hydrate.
Whisk flour, baking powder, baking soda, salt, and cinnamon in a separate bowl.
Beat brown sugar, oil, egg, vanilla, and molasses in a large bowl until smooth.
Stir the soaked bran mixture into the wet ingredients until combined.
Fold in the dry ingredients just until no dry streaks remain, then gently fold in raisins.
Divide batter among cups, filling each about 3/4 full.
Bake 16–19 minutes until a toothpick comes out clean. Cool 5 minutes, then transfer to a rack.