Preheat the oven to 350°F. Generously grease one or two standard donut pans.
To a large mixing bowl add the oil, eggs, sugar, pumpkin, spices, salt, and baking powder. Beat together on low speed until smooth.
Mix in the flour by hand just until combined - over mixing will cause them to be rubbery.
Scoop up scant ¼ cups of the batter to fill each well of the donut pan. If you only have one pan cover the batter with saran wrap and let it sit in a cool place in between batches.
Bake 15 to 18 minutes or until a toothpick comes out clean from the center.
Cool in the pan 5 - 10 minutes then turn out from the pan running a knife around the edges if needed.
Let them cool completely.
In a wide shallow bowl mix the sugar and cinnamon together. Alternately you can add it to a large plastic food bag and shake the donuts in it.
Working one at a time use a pastry brush to coat the donuts in butter then dip them in cinnamon sugar or shake them in the bag of cinnamon sugar.
Loosely cover the leftovers and store in a cool, dry place up to 3 days.