Preheat your oven to 375°F (190°C). Grease a muffin tin or line with paper liners.
In a large bowl, mix together the oat bran, flour, brown sugar, baking powder, baking soda, and salt.
In another bowl, whisk together the buttermilk, vegetable oil, egg, and vanilla extract.
Pour the wet ingredients into the dry ingredients and stir until just combined.
Divide the batter evenly among the muffin cups.
Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the tin for a few minutes, then transfer to a wire rack to cool completely.