Blot the Pumpkin Purée (Crucial Step): Spread 1/2 cup pumpkin purée between several layers of paper towels and gently press out excess moisture until reduced to about 1/3 cup. This prevents cakey cookies and ensures a chewy, pillowy snickerdoodle texture!

Cream Butter & Sugars: In a stand mixer or large bowl with a hand mixer, beat softened butter, granulated sugar, and brown sugar on medium speed for 2 minutes until creamy and fluffy. Beat in egg yolk, vanilla extract, and blotted pumpkin purée until well combined.

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

Combine & Chill: Add dry ingredients to wet mixture and mix on low speed just until dough forms. Cover and chill dough in refrigerator for 30 minutes for easy rolling.

Roll in Spiced Sugar: Preheat oven to 350°F (175°C). Line two baking sheets with parchment paper. In a small bowl, whisk together the coating ingredients (sugar, cinnamon, pumpkin pie spice). Scoop 1.5-tablespoon portions of dough, roll into balls, and generously roll in the spiced sugar until fully coated.

Bake to Perfection: Place dough balls 2 inches apart on prepared sheets. Gently flatten tops slightly with the bottom of a glass. Bake for 9 to 11 minutes until edges are set but centers are still soft and pillowy. Do not overbake!

Cool: Cool on baking sheet for 5 minutes, then transfer to a wire cooling rack. The cookies will crinkle and settle as they cool.