Preheat oven to 200 degrees C and grease a 12 cup muffin tin.
In a bowl, combine milk and bran. Set aside. In another bowl, sift flour, baking powder and salt.
With an electric beater, combine sugar and eggs. Add the vanilla and banana. Beat until smooth and slightly frothy then add the milk and bran. Add the raisins, chocolate chips and melted butter.
Add the flour all in one go and beat just until everything is combined. Do not overbeat it or the muffins will be tough. Spoon into muffin cups to 2/3 full.