Preheat the oven to 350°F and line a baking sheet with parchment paper.

In a large bowl, mix the sugars and melted butter until smooth and well combined.

Stir in the pumpkin puree, egg, and vanilla extract until fully incorporated.

In a separate bowl, whisk together the flour, cornstarch, cream of tartar, baking soda, pumpkin pie spice, cinnamon, and salt.

Gradually fold the dry ingredients into the wet ingredients until a soft dough forms.

Portion and roll the dough into small balls.

In a small bowl, combine the sugar and cinnamon. Roll each dough ball in the cinnamon sugar mixture.

Arrange them on the prepared baking sheet.

Bake for 10 to 12 minutes, or until the edges are set and the centers are still soft.