Preheat oven to 350 degrees. Spray donut pans with non-stick cooking spray.
In a large bowl add all ingredients through the baking powder, beat with mixer on medium speed until smooth. Add the flour stirring until smooth.
Fill the wells of the donut pans about 3/4 full. Bake donuts 15 to 18 minutes, or until a toothpick inserted comes out clean.
Remove donuts from the oven, after about 5 minutes, loosen their edges, and transfer them to a rack to cool.
While donuts are still warm, but no longer fragile, quickly dip them on each side in the melted butter, then gently shake them in a bag with the sugar and cinnamon mixture.
Notes
Best if not stored in a plastic bag they may become soggy.