2. Sift the flour, sugar, baking soda and salt together. (This can be done the night before and kept covered on the counter.)
3. Whisk together the eggs, buttermilk and bran. Let stand for 10 minutes.
4. Make a well in the center of the dry ingredients and add the egg mixture all at once. Stir with a wooden spoon until the dry ingredients are just moistened.
5. Fold in the mashed banana. (Be careful to keep the mixing to a minimum -- a light stirring which will leave some lumps is fine. The dough should not be mixed to the point of pouring, but should break in coarse globs.) Fill the tins two-thirds full, being careful not to drip the batter on the edge of the tins where it will burn and cause sticking.
6. Bake in the prepared muffin tins for about 25 minutes. The muffins are done when a knife inserted in the center of a muffin comes out dry.