Blot the pumpkin puree: Spread the ½ cup pumpkin puree on a plate lined with 4 layers of paper towels. Press gently with more paper towels to absorb excess moisture until you have roughly ⅓ cup concentrated puree. This is the key to chewy, non-cakey cookies!

In a medium bowl, whisk together the flour, pumpkin pie spice, cream of tartar, baking soda, and salt. Set aside.

In a large bowl, whisk the melted butter, brown sugar, and granulated sugar together until smooth. Whisk in the blotted pumpkin puree, egg yolk, and vanilla extract until glossy.

Pour the dry ingredients into the wet ingredients and fold with a wooden spoon or rubber spatula just until no flour streaks remain. Chill the dough in the refrigerator for 30 minutes.

Preheat oven to 350°F (175°C). Line two large baking sheets with parchment paper. In a small bowl, mix the ⅓ cup granulated sugar and 1.5 teaspoon cinnamon.

Scoop 2 tablespoon portions of dough (approx 45g each) and roll into smooth balls. Roll each ball generously in the cinnamon sugar coating until completely covered.

Place balls 2 inches apart on the baking sheets. Bake for 10 to 12 minutes until edges are set and tops are crinkled and cracked (centers will look slightly soft).

Remove from oven and let cookies cool on the baking sheet for 10 minutes before transferring to a wire rack to cool completely. The centers remain melt-in-your-mouth soft!