In a medium bowl, whisk together flour, cornstarch, cream of tartar, baking soda, baking powder, salt, cinnamon, ginger, nutmeg and allspice until combined. Set aside.
In the bowl of an electric stand mixer (or using a hand mixer), beat together butter, granulated sugar and brown sugar on medium speed just until combined, about 30 seconds. Mix in egg yolk, then add pumpkin and vanilla extract. Again, mix until just combined. Scrape down the sides of the bowl if necessary.
With mixer set on low speed, slowly add in dry ingredients then mix until combined. Cover the bowl with plastic wrap and chill for 1 hour.*
Ten minutes before removing dough from the refrigerator, preheat oven to 350° F. Line baking sheet with parchment paper.
To make the cinnamon sugar coating, whisk together 1/4 cup granulated sugar with 2 teaspoons cinnamon. Scoop a generous tablespoon of dough and shape into a ball, roll dough ball in cinnamon sugar to evenly coat. Set ball of dough on prepared baking sheet. Repeat with remaining dough spacing cookies 2-inches apart.
Bake in preheated oven 12 to 14 minutes or until cookies are set and edges are golden brown. Cool on baking sheet about 5 minutes then transfer to a wire rack to cool completely.
Storing pumpkin snickerdoodles: Store baked cookies at room temperature in an airtight container for up to 5 days or in the refrigerator for up to one week.Chilling pumpkin snickerdoodle cookie dough: Dough can be chilled up to 24 hours. Let it sit on the counter for 15 or so minutes until the dough is soft enough to scoop and you can roll it into balls.Freezing pumpkin snickerdoodle cookie dough: Wrap dough in plastic wrap and store in the freezer for up to 3 months. Defrost in the refrigerator before scooping into balls and baking.Recommended Tools:
Kitchen scale to weigh ingredients (it's more accurate than measuring).