Sift all the dry ingredients together for the doughnuts into a large bowl.
In another bowl whisk together the eggs, vanilla, buttermilk, and melted butter. Stir the buttermilk mixture into the flour mixture, just until combined.
Spoon the batter into a doughnut formed baking pan, sprayed with cooking spray, to about ¾’s full for each doughnut. (A cake decorating tool or plastic bag with the corner cut works really good for this.) Bake the doughnuts for 17 minutes or until a toothpick inserted comes out clean.
While the doughnuts are baking prepare the topping by melting 1 stick of butter in a saucepan on low heat. In a small bowl mix together the cinnamon and sugar and set aside.
When the doughnuts are done let them cool for several minutes and then turn the pan over to remove the doughnuts. (Careful, they are round, and like to roll)
Dip the doughnuts into the butter, and then the sugar, on one side, or both. Enjoy