In one bowl combine the buttermilk and bran flakes. Let sit for about 10 - 15 minutes, stirring occasionally.
In a separate bowl whisk together the oil, eggs, both sugars and vanilla.
Then stir in the bran mixture and raisins. Mix well.
In a separate bowl, whisk together the flour, baking soda, baking powder and salt.
Combine the bran mix with the flour mix.
Fill muffin cups about 2/3 full.
Bake for 25 minutes.
Notes
This batter can be kept in the fridge for up to 2 weeks. So you can bake as big or small batches as you would like! All together, you can get about 24 good sized muffins from this batter.