Line a muffin tin with liners. Use regular-size muffin tins, or jumbo size. We like the jumbo muffins and this bran muffin recipe holds up well in a larger size.
In large mixing bowl, whisk together the flour, baking soda, salt, and white and brown sugars.
Place cereal in separate bowl, and crunch the bran flakes into smaller pieces. Your your hands and just crush the cereal.
Add crushed cereal to flour mixture and stir to combine.
In medium bowl, mix together the buttermilk, vegetable oil, egg, and vanilla. Stir to combine.
Pour the wet ingredients into the dry ingredients and stir to combine.
Let the combined muffin mix sit on the counter for about 40 minutes to allow the wet mixture to soften the cereal. You can also refrigerate the batter and use another time.
Pour batter into prepared muffin tins, filling 3/4 high. Sprinkle tops of muffins with sugar (your choice, use white sugar, brown sugar, or both).
Bake for 15-20 minutes or until a toothpick inserted comes out clean.