Add the flour, cornstarch, cream of tartar, baking soda, salt and pumpkin pie spice to a large mixing bowl and mix with a whisk.

In the bowl of your stand mixer, add the granulated sugar, brown sugar and softened butter. Mix well on medium speed until nice and creamy (about 3-4 minutes), using the paddle attachment.

Add the egg, pumpkin, and vanilla and mix on low speed.

Add the flour mixture, a cup at a time to the mixture, on low speed, until combined.

Cover with plastic wrap and refrigerate for 2 hours (or more).

Preheat the oven to 350°F.

In a small bowl, mix the cinnamon sugar mixture together.

Using a cookie scoop, take 1 scoop of the refrigerated cookie dough, roll into a ball then roll in the cinnamon sugar.

Place on a cookie sheet lined with parchment paper and using the back of a cup flatten a little. Repeat until cookie sheet is filled (2” apart) - try to work quickly or the cookie dough will get soft to handle. If that happens, refrigerate again between batches.

Bake for 8-10 Minutes.

Allow to sit on cookie sheet for 5 minutes, before transferring to a wire rack to cool.