Preheat the oven to 350°F (180°C). Spray your donut pan with non-stick spray and set aside.
Make the vegan buttermilk. In a small bowl, stir together the non-dairy milk of your choice and the apple cider vinegar. Set aside for 5 minutes.
Mix the dry ingredients. Whisk the flour, cornstarch, baking powder, baking soda, salt, and pumpkin pie spice together in a medium bowl until combined. Set aside.
Mix the wet ingredients. In a large bowl, whisk together the pumpkin, brown sugar, oil, milk mixture, and vanilla until they are combined.
Combine. Pour the dry ingredients into the wet and then fold them together gently until just combined.
Transfer to donut pan. Carefully spoon the batter into the donut pan. Or, fill a piping bag with the batter and pipe the batter into each donut cup, filling about ¾ of the way full.
Bake for 12-14 minutes until the tops are golden brown and the donuts have pulled away from the edges of the pan. Remove from the oven and immediately remove them from the pan and coat with cinnamon sugar.
Cool and enjoy! Let the donuts cool slightly on a wire rack before enjoying. Cover leftover donuts tightly and store at room temperature for 1-2 days or up to a week in the fridge. Enjoy!
