Preheat oven to 400 degrees. Place rack in the middle of the oven. Line 12 muffin cups with paper liners.
In a medium-sized bowl, mix together the pumpkin puree, eggs, buttermilk, oil and vanilla extract. Set aside.
In a large mixing bowl, combine the flour, bran, sugar, baking powder, baking soda, cinnamon and salt. Add the milk and egg mixture to the flour mixture. Stir until just combined. Fold in raisins or dried cranberries if you wish. Do not overmix the batter.