Mix bran and buttermilk in a large bowl and let rest for 5 minutes.
Mix in oil, sugar, egg, banana, and vanilla.
In a medium bowl, whisk flour, baking soda, baking powder, and salt together. Add to bran mixture and stir until just combined. Gently fold in blueberries.
Add batter to prepared muffin tin. Bake 20-25 minutes. Let cool for 5 minutes then remove from muffin tin.
Notes
Blueberry bran muffins will keep fresh up to 4 days in an airtight container.Place a piece of bread or paper towel in the container with the muffins to soak up the moisture.