Preheat the oven to 375°F (190°C or 180°C for a fan oven)
Grease or put paper liners in a 12 cup muffin pan.
Beat eggs in a large bowl.
Add brown sugar and oil. Mix well.
Sir in bran and cinnamon.
Let the mixture stand for ten minutes.
Meanwhile, sift together the flour, baking soda, cream of tartar and salt.
Add the flour mixture to the bran mixture alternately with the buttermilk. Do this in four additions - two of the flour mixture and two of the buttermilk, ending with the buttermilk.
Fold in the raisins.
Fill muffin cups half full with batter.
Bake for 18 to 20 minutes or until a skewer inserted in the centre comes out clean.