Preheat your oven to 350°F (175°C) and grease your donut pan with cooking spray or butter.
In a mixing bowl, whisk together the all-purpose flour, baking powder, ground cinnamon, ground nutmeg, and salt until well combined.
In another bowl, combine the pumpkin puree, granulated sugar, brown sugar, eggs, milk, and melted butter. Mix until smooth.
Gradually add the dry ingredients to the pumpkin mixture, gently folding until just combined. Be careful not to overmix. The batter should be thick.
Transfer the batter to a piping bag or a zip-top plastic bag with one corner snipped off. Pipe the batter into the prepared donut pan, filling each cavity about ⅔ full.
Bake for 12 to 15 minutes, or until the donuts are golden and a toothpick inserted into the center comes out clean.
While the donuts are baking, mix together the remaining ¼ cup granulated sugar and 1 teaspoon ground cinnamon in a small bowl to create the cinnamon sugar coating.
Allow the donuts to cool in the pan for a few minutes before transferring them to a cooling rack. Once slightly cooled, coat each donut in the cinnamon sugar mixture, ensuring they are completely covered.
Serve warm or at room temperature. Enjoy your delicious pumpkin cinnamon sugar donuts!