1) In a small mixing bowl, pour the boiling water over the half cup of cereal. When cooled, mix in the vegetable oil and egg.
2) While the water/bran mixture cools, whisk together the flour, sugar, baking soda, baking powder and salt in a large mixing bowl. Stir in the raisins.
3) In a large measuring cup, combine the buttermilk and brown sugar, and stir into the dry ingredients. Stir in remaining cereal, then the softened bran mixture. Cover the batter and refrigerate it overnight.
4) When you're ready to bake, preheat the oven to 375°F for 15 minutes. Line a muffin tin with papers, and spray the insides of the papers. Or just grease the muffin cups themselves, if you like a crustier muffin edge.
5) Stir the batter once or twice, then scoop a heaping 1/4-cup of batter into each prepared muffin cup.
6) Bake for 20 to 25 minutes, until a tester inserted in the center comes out clean.
7) Remove from the oven, cool in the pan on a rack for 10 minutes before removing the muffins from the pan.