Blot Pumpkin Puree: Preheat oven to 350°F (177°C) and line two large baking sheets with parchment paper. Spread the pumpkin puree onto 3-4 layers of paper towels, fold over, and gently press to blot out excess liquid until reduced to a thick, concentrated paste. This is essential for chewy cookies instead of cakey ones.

Whisk Dry Ingredients: In a medium mixing bowl, whisk together the flour, cream of tartar, baking soda, sea salt, pumpkin pie spice, and cinnamon until well combined.

Combine Wet Ingredients: In a separate large bowl, whisk the melted butter, brown sugar, and granulated sugar until glossy. Whisk in the blotted pumpkin puree, egg yolk, and vanilla extract until completely smooth and emulsified.

Fold & Chill Dough: Fold the dry ingredients into the wet mixture using a silicone spatula just until combined and no dry streaks remain. Cover and chill in the refrigerator for 20 to 30 minutes to make shaping effortless.

Roll in Cinnamon Sugar: In a shallow bowl, whisk together the cinnamon and sugar for the coating. Scoop 1.5-tablespoon portions of dough, roll into smooth balls, and roll thoroughly in the cinnamon sugar mixture until generously encrusted. Place dough balls 2 inches apart on prepared sheets.

Bake to Chewy Perfection: Bake at 350°F for 9 to 11 minutes until the edges are lightly golden and set, and the tops are crinkled and puffed. The centers will look very soft. Cool on the baking sheet for 5 minutes, then transfer to a wire rack to set completely. Enjoy warm!