Combine the dry ingredients: Whisk together flour, cream of tartar, pumpkin pie spice, baking soda, and salt in a medium bowl.
Combine the wet ingredients: Whisk together melted butter, pumpkin purée, brown sugar, granulated sugar, egg yolk, and vanilla extract until smooth.
Make the batter: Fold dry ingredients into wet ingredients until just incorporated.
Chill: Cover and chill the dough in the refrigerator for at least 30 minutes.
Preheat the oven to 350°F. Line 2 baking sheets with parchment paper.
Make the pumpkin spice sugar mixture: Whisk together granulated sugar and pumpkin pie spice in a shallow bowl.
Shape the cookies: Use a cookie scoop or tablespoon to portion and shape the dough. Roll each scoop in the sugar mixture and space evenly on baking sheets.
Bake: Place a pan on each rack in the oven and bake for 11 to 12 minutes, rotating pans halfway through. The edges of the cookies will be set, and the tops will look puffed and cracked.
Cool and serve: Let the cookies cool on the pan for 5 minutes, then transfer them to a wire rack to cool completely.
Store: Keep in an airtight container at room temperature for up to 5 days.