Preheat oven to 375°F/190°C. Grease a 6 cup jumbo muffin pan or line with muffin cups. You can also use a 12 cup pan.
In a small bowl combine natural bran and buttermilk. Allow to soak for 10 minutes. After 10 minutes add eggs. Whisk together until mixture is smooth. Add brown sugar, oil, molasses and vanilla. Stir until well blended.
Add all purpose flour, baking powder, baking soda, cinnamon and salt. Mix with a spatula until just combined or until there are no traces of dry flour remaining. Do not over mix.
Divide batter evenly among cups, filling almost to the top. The muffins will grow quite a bit, so do not make the cups too full. Bake for 18-20 minutes or until a toothpick inserted in the center of one of the muffins comes out clean. If making 6 jumbo muffins, it may take a few minutes longer.
Allow muffins to cool in pan for 10 minutes before removing onto wire rack to cool completely. Serve warm or store at room temperature for up to 4 days.
Notes
You do not need to make jumbo sized muffins if you don't want to. For smaller muffins, divide among 12 muffin cups and check if done after 16-18 minutes of baking.For raisin bran muffins, soak 1 cup of raisins in boiling water for 10 minutes. Drain and add to batter while mixing in dry ingredients.