For the Donuts:

1. Preheat the oven to 325°F and spray a donut pan with nonstick spray.
2. Whisk together the flour, baking powder, baking soda, spices, and salt in a medium bowl.
3. In another bowl, whisk together the sweet potato, sugar, egg, oil, and vanilla. Slowly fold the dry ingredients into the wet and mix until just combined.
4. Transfer the batter to a resealable plastic bag (or piping bag) and cut off one corner. Squeeze the batter into the prepared donut pan, filling each donut well about ¾ full. You can also spoon the batter into the pan – just ensure you smooth the batter very well to avoid broken donuts.
5. Bake the donuts for 12-15 minutes or until the donuts are set and spring back slightly when lightly pressed. Cool the donuts in the pan for a few minutes and then transfer to a cooking rack to cool completely.
6. I have a 6-well donut pan, so I repeated this process with the remaining batter until it was all baked. This recipe yields roughly 8 donuts.

For the Coating:

1. Melt and cool the butter.
2. In a bowl, whisk together the sugar and the cinnamon until completely combined.
3. When the donuts are cool enough to handle, brush lightly with the melted butter and then turn them to coat in the cinnamon-sugar mixture. Return to the rack and allow the excess to fall off. Repeat with all the donuts. Store donuts in an airtight container at room temperature for up to 3 days.