Preheat oven to 375 degrees F (190 degrees C). Grease muffin cups or line with paper muffin liners.
Mix together wheat bran and buttermilk; let it stand for 10 minutes or more.
Beat together oil, egg, sugar and vanilla and add to buttermilk/bran mixture. Mix well.
Sift together flour, baking soda, baking powder and salt. Stir flour mixture into buttermilk mixture, until just blended.
Mix in the raisins and/or the chocolate chips.
Spoon the batter into the muffin cups.
Bake for 15 to 20 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Let the muffins cool, and then enjoy with a hot cup of tea or coffee!