Blot the pumpkin puree: Spread 6 tablespoons of canned pumpkin puree across a double layer of paper towels on a plate. Press gently with a second double layer of paper towels to absorb excess moisture until the pumpkin measures approximately 1/3 cup of thick, concentrated paste.

In a large mixing bowl, whisk together the melted butter, brown sugar, and granulated sugar until smooth and completely combined.

Whisk in the blotted pumpkin puree, egg yolk, and pure vanilla extract until velvety smooth and glossy.

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

Pour the dry ingredients into the wet mixture and fold gently with a wooden spoon or silicone spatula just until a soft, uniform dough forms. Do not overmix.

Cover the bowl with plastic wrap and chill the dough in the refrigerator for at least 45 minutes (or up to 48 hours). Chilling is crucial to prevent the cookies from over-spreading in the oven.

Preheat your oven to 350°F (175°C). Line two large baking sheets with parchment paper or silicone baking mats.

Prepare the coating: In a small shallow bowl, stir together 3 tablespoons of granulated sugar, 1 teaspoon of cinnamon, and 1/2 teaspoon of pumpkin pie spice.

Scoop 1.5 tablespoon balls of chilled dough (using a #40 cookie scoop) and roll gently between your palms into smooth balls. Roll each ball generously in the cinnamon sugar mixture until thoroughly coated.

Arrange the dough balls 2 inches apart on the prepared baking sheets. Lightly flatten each ball slightly with your fingertips so they spread evenly.

Bake at 350°F (175°C) for 10 to 12 minutes, until the edges are lightly golden and set, and the centers are puffed and slightly crinkled. The centers will still look very soft.

Remove from the oven and allow the cookies to cool on the warm baking sheet for 10 minutes (they will finish setting into chewy perfection). Transfer to a wire rack to cool completely.