Muffins
Preheat the oven to 400F
Add the egg, milk, butter, sweet potato, and vanilla to a medium bowl. Stir well to combine.
Stir in the rest of the ingredients and spoon into prepared donut pan, filling each full. (You'll use a heaping ¼ cup batter in each.)
Bake for 16-18 minutes for donuts or 10-13min for mini-muffins, until lightly golden brown around the edges and a cake tester inserted into the center comes out clean.
Remove from oven, let sit for 2-3 minutes, then invert onto a wire rack to cool slightly.
For the frosting: Stir together ¼ cup plain Greek yogurt, 2 tablespoons milk, 2 tablespoons honey, ¼ teaspoon vanilla extract, and a pinch of pumpkin pie spice until smooth in a wide bowl. Dunk one side of each donut in the frosting, then place onto a wire rack. Add sprinkles if desired. (Place a piece of parchment underneath to catch any drips.)
