Spread the pumpkin purée across a plate lined with 4 layers of paper towels. Press another 2 paper towels firmly on top to absorb excess moisture until the purée feels thick and paste-like. Measure out ⅓ cup of blotted pumpkin.

In a large mixing bowl, whisk together melted butter, brown sugar, granulated sugar, blotted pumpkin purée, egg yolk, and vanilla extract until completely smooth, glossy, and emulsified.

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

Pour dry ingredients into the wet mixture and fold gently with a rubber spatula just until no flour streaks remain. Cover bowl and chill dough in the refrigerator for 30 minutes to firm up slightly for easy rolling.

Preheat oven to 350°F (175°C). Line two large baking sheets with parchment paper. In a small shallow bowl, stir together ⅓ cup granulated sugar and 1 ½ tablespoons ground cinnamon.

Scoop dough using a 1 ½-tablespoon cookie scoop and roll into smooth balls. Roll each ball generously in the cinnamon sugar mixture until heavily coated on all sides.

Arrange dough balls 2 inches apart on the baking sheets. Bake at 350°F for 9 to 11 minutes until edges are set and tops are crinkled and puffed. Do not overbake; the centers should still look very soft!

Immediately after pulling the baking sheet from the oven, gently tap or bang the pan on the counter 2 to 3 times to collapse the cookies slightly and create signature crinkly ripples. Let cookies cool on the sheet for 10 minutes before transferring to a wire rack to set.