In a small bowl, measure the gluten-free flour. This is best done with the "spoon and level" method. Lightly spoon the flour into the measure cup and then use a flat edge to level off the excess. 

To the flour add the baking soda, cream of tartar, and salt. *When making the batter, I thought it was too wet and added the cornstarch. I would suggest baking one or two cookies prior to adding it. However, corn starch often adds a softness to cookies that is wonderful! *

In a separate larger bowl, cream the butter and sugars together. Next, add the pumpkin. (Make sure it is not super cold, as cold pumpkin will harden the butter.) 

Finally, instead of adding traditional vanilla, use up to 2 tbsp chai concentrate. As these cookies do not contain egg, you can add the chai concentrate to taste. Place batter in refrigerator and allow to firm for at least an hour. (Most gluten-free cookie batters benefit from refrigeration.) 

Remove batter from refrigerator. Preheat oven to 350 degrees. 

In a small container, mix together the Chai Spice Sugar ingredients. Using a large tablespoon, scoop out some batter, and roll between palms to create a ball. Next, coat dough ball in Chai Spice Sugar blend. Next, flatten the dough ball between your palms. Finally, if desired, coat the flattened cookie with an extra dusting of the Chai Spice Sugar. I highly recommend it! 

Bake cookies at least an inch apart on a parchment lined cookie sheet. Bake for 10 - 12 minutes. (I accidentally baked one batch for 16 minutes and they still turned out just fine. I assume this is due to the moisture in the pumpkin.) 

Allow cookies to cool on cookie sheet for 5 minutes, then transfer to a cooling rack. Makes approximately 2 dozen cookies.