In a large mixing bowl, combine pumpkin, bran cereal, butter, and sugars. Stir in the eggs and yogurt. In a separate bowl, whisk together the flour, salt, spices, baking soda and baking powder. Stir into the pumpkin mixture, then stir in the raisins. Cover the bowl and refrigerate the batter for 4 hours or overnight.
Preheat the oven to 375°F Lightly grease muffin pan. Scoop the batter into the pan, using a heaping 1/4 cup of batter for each. Bake in for 25-28 minutes. Remove the muffins from the oven and cool in pan for five minutes. Take them out of the pan and finish cooling on a rack.