In a large bowl, stir together the pumpkin, brown sugar, oil, buttermilk, and butter. Beat in the eggs.
In a separate bowl, combine the flour, baking powder, baking soda, salt, and pumpkin pie spice. Add to the wet ingredients and mix until just combined.
Spoon the batter into a piping bag or a ziplock bag with one corner snipped off.
Squeeze the batter into prepared donut pans sprayed with nonstick cooking spray. Fill about 3/4 full.
Bake at 350° Fahrenheit for 25-30 minutes, until a toothpick inserted into the center should come out clean. Let cool in the pan for about 5 minutes and then remove onto a cooling rack.
Cinnamon Sugar Coating
Once cool to touch, dip both sides of each pumpkin donut in melted butter and then cinnamon-sugar mixture. I let them dry and then re-dip each doughnut in the cinnamon-sugar mixture for a more even coat!
Donut Storage
Donuts taste best eaten the same day. If not, keep the unsugared donuts in a ziplock bag in the freezer until use, up to two weeks. Let defrost on the counter an hour before eating.