Pour boiling water over ¾ cup of the bran cereal in a small mixing bowl. Add the raisins, brown sugar and oil. While the bran mixture cools, whisk together the flour, baking soda, baking powder and salt in a large mixing bowl.
Beat the egg with the buttermilk and orange juice in a large measuring cup. Add this mixture to the dry ingredients. Stir in the remaining ½ cup bran cereal, then the bran/raisin mixture. Cover the bowl and refrigerate overnight.
The next day, preheat oven to 375°F. Lightly grease a muffin tin or line with papers and coat the papers with nonstick spray.
Fill each cup two-thirds full with batter. Bake the muffins until a cake tester inserted in the center comes out clean, 23 to 26 minutes for regular-sized muffins (35 to 40 minutes for jumbo muffins).
Remove from oven and allow the muffins to cool in the pan for 5 minutes, then turn them out onto a rack to finish cooling, or serve warm, as desired.
Notes
The batter can be mixed up and held in the refrigerator for up to a week, then scooped and baked as needed, so you can have fresh, warm muffins whenever you like!
If you prefer, you can make 6 jumbo muffins instead of the 12 regular sized.