Preheat your oven to 375°F (190°C) and line a muffin tin with paper liners or grease it lightly.

In a large bowl, combine the wheat bran and buttermilk. Let it sit for about 10 minutes to soften the bran.

Add the brown sugar, honey, and egg to the bran mixture. Mix until well combined.

In a separate bowl, whisk together the whole wheat flour, baking soda, and salt.

Gradually add the dry ingredients to the wet ingredients, stirring until just combined. Do not overmix.

If using, fold in the raisins and walnuts until evenly distributed.

Spoon the batter into the prepared muffin tin, filling each cup about two-thirds full.

Bake for 18-20 minutes, or until a toothpick inserted in the center comes out clean. Let cool in the pan for 5 minutes before transferring to a wire rack.