Preheat your oven to 350 degrees F.
Coat 2, 24-count mini muffin pans with non-stick spray.
In a mixer, combine the sugar and butter until it’s fluffy. Add the egg, pumpkin puree and buttermilk (or substitute), and again, beat until the mixture is smooth.
Add the dry ingredients together into a bowl and whisk until everything is thoroughly combined.
Add the dry ingredients to the batter a bit at a time, and blend until it’s smooth.
Use a tablespoon to drop the batter into the muffin tins. I suggest you don’t fill the dough to the top of the tin -- leave a bit of room for them to “grow.”
Bake for about 15 minutes, or until a toothpick inserted into the center of the doughnut holes comes out clean.
Remove the doughnut holes from the tins and allow them cool on a wire rack. Meanwhile, melt the butter for the coating, and in a separate bowl, mix the sugar and cinnamon together.
Use a pastry brush to LIGHTLY coat each doughnut hole with the melted butter. If you use too much butter, the holes will get soggy.
Immediately after (lightly) coating each with the butter, role the holes in the cinnamon-sugar mixture to coat each hole all the way “around.”