1. Preheat oven to 350 degrees F. Spray 30 muffin cups with nonstick spray.
2. In a small bowl, mix together the bran flakes cereal and sour cream. Let stand for 10 minutes.
3. In a medium bowl, whisk together the olive oil, eggs, sugar and vanilla.
4. In another bowl, whisk together the flour, baking soda, baking powder, and salt.
5. Stir the sour cream/bran mixture into the egg mixture. Add the flour mixture. Add in the raisins and chopped walnuts. Spoon the batter into the muffin cups.
5. Bake 15 minutes, or until a toothpick inserted into the center of a muffin comes out clean.