Preheat the oven to 375 degrees F, and grease or line a 12-cup muffin tin. (If using paper liners, I recommend spraying them with cooking spray so the paper doesn’t stick to the muffin. This is somewhat common with gluten-free flours.)
In a large mixing bowl, combine the pumpkin, crushed cereal, raisins, butter or melted coconut oil, and sugars. Stir in the eggs and the buttermilk.
In another bowl, whisk together the flour, cinnamon, nutmeg, baking soda, baking powder, and salt. (Stir in the optional nuts and/or coconut at this point.) Add to the pumpkin mixture and stir to combine.
Scoop the batter into the prepared muffin cups. I like to use a large ice cream scoop. The cups will be rather full but they will not overflow.
Sprinkle the tops with a little coarse sugar or shredded coconut, if desired. (The muffins will still be delicious if omitted.) Then bake for 23-28 minutes or until the muffins pass the toothpick test and do not feel mushy in the center when the top of the muffins are gently pressed. (Check a little early as all ovens vary.)
Allow the muffins to cool for 5 minutes in the pan, and then remove to a rack to cool completely.
Once cool, frost with the maple cream cheese frosting, if using. Store the muffins in an airtight container in the refrigerator.