Preheat oven to 375°F (190°C). Grease and flour a 12-cup muffin tin, or line with paper liners.
In a large bowl, whisk together the flour, wheat bran, brown sugar, baking soda, salt, and cinnamon.
In a separate medium bowl, whisk together the buttermilk, vegetable oil, and egg.
Pour the wet ingredients into the dry ingredients and stir until just combined. Do not overmix.
Divide the batter evenly among the prepared muffin cups.
Bake for 18-20 minutes, or until a wooden skewer inserted into the center of a muffin comes out clean.
Let the muffins cool in the tin for a few minutes before transferring them to a wire rack to cool completely.
Notes
These muffins can be stored in an airtight container at room temperature for up to 3 days, or in the refrigerator for up to a week. They also freeze well.