Preheat oven to 350°F (175°C). Lightly grease a mini donut pan.
In a large bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, and pumpkin pie spice.
In another bowl, whisk together the sugar, pumpkin purée, milk, yogurt, egg, vanilla, and melted butter/oil until smooth.
Add the wet ingredients to the dry ingredients and stir until just combined—don’t overmix.
Put pumpkin donut batter in a piping bag with no tip (or a plain round tip) and pipe the batter into the donut pan, filling each cavity about 3/4 full. Alternatively, you can spoon the batter in, but it gets pretty tricky with mini donuts.
Bake for 8–10 minutes, or until the donuts spring back when lightly touched and a toothpick comes out clean.
Let cool for a few minutes in the pan, then transfer to a wire rack.
While the donuts are still slightly warm, brush them with melted butter and immediately roll (or sprinkle) them in the cinnamon sugar mixture. For best results, do this one donut at a time so the sugar sticks well.