Preheat the oven to 350°F. Grease the donut pan with nonstick spray or melted butter and set aside.
Whisk the flour, baking powder, baking soda, salt, cinnamon, and pumpkin pie spice in a large bowl and set aside.
In a medium bowl, whisk the oil, brown sugar, eggs, pumpkin puree, milk, and vanilla until smooth. Add the sourdough discard and mix lightly until just combined.
Pour the dry ingredients into the wet ingredients and whisk gently until the batter is combined and no flour pockets remain. Do not over mix.
Spoon or pipe the batter into the donut pan, filling each cavity about halfway.
Bake for 10 to 11 minutes or until the tops and edges are lightly browned and the donuts spring back when touched.
Let the donuts cool in the pan for 2 minutes, then transfer to a cooling rack.
In a small bowl, combine granulated sugar, brown sugar, and pumpkin pie spice. Stir until evenly mixed.
When the donuts have cooled, dip each side into the sugar mixture until fully coated. Return the donuts to the cooling rack and enjoy!