Preheat oven to 375°F. Grease muffin tin with nonstick spray and set aside.
Mix together the wheat bran and buttermilk in a large bowl and let sit for 10 minutes.
1½ cups wheat bran, 1 cup buttermilk
In a separate bowl, beat together the apple sauce, egg, brown sugar, and vanilla until combined.
⅓ cup apple sauce, 1 large egg, ⅔ cup light brown sugar, ½ teaspoon vanilla extract
Add to the bran mixture and mix just until combined.
Sift the flours, baking soda, baking powder, and salt on top of the wet ingredients.
½ cup all-purpose flour, ½ cup whole wheat flour, 1 teaspoon baking soda, 1 teaspoon baking powder, ½ teaspoon salt
Then stir the flour mixture into the wet ingredients, until just combined.
Add ½ cup of batter to 8 greased muffin cups and sprinkle some additional bran on top, if desired.
Bake for 15 to 20 minutes or until a toothpick inserted into the center of a muffin comes out clean.