• Combine cooled melted butter, sugar, and brown sugar until well combined. Ensure butter is not warm to the touch to prevent sugar from melting.
• Mix in pumpkin puree, egg yolk, and vanilla extract.
• In a separate bowl, whisk together flour, pumpkin pie spice, baking soda, cream of tartar, and salt.
• Gradually add the dry ingredients to the wet mixture until just combined.
• Cover the dough and refrigerate for at least 45 minutes. This chilling time is crucial for texture.
• Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. Prepare the topping by mixing sugar and cinnamon in a shallow dish.
• Scoop dough into 1 ½ tablespoon-sized balls, roll them smooth, and then roll through the cinnamon-sugar mixture. Place the balls on the prepared baking sheet at least 2 inches apart.
• Bake for 10-12 minutes, or until the edges are lightly golden. Keep the remaining dough refrigerated while baking.
• Allow the cookies to cool completely on the baking sheet before serving to achieve the perfect chewy texture.

Notes

• Use pure pumpkin puree, not pumpkin pie filling, for the best flavor and texture. Ensure melted butter is cooled before mixing with sugar to prevent it from melting.
• Using only the egg yolk helps control moisture from the pumpkin. Cream of tartar is essential for the classic snickerdoodle flavor and texture.
• Dough can be refrigerated for up to 3 days or frozen unbaked for later use. If dough is too firm, let it sit at room temperature briefly before scooping.
• Consider making a double batch, as these cookies are often a fast favorite.