Preheat oven to 350 degrees. Line baking sheets with parchment.
In a small mixing bowl, whisk together flour, baking soda, cream of tartar, pumpkin pie spice, and salt; set aside.
In a large mixing bowl, using a handheld electric mixer set on medium speed, cream together powdered sugar, granulated sugar, and butter, until light and fluffy, about 2 minutes.
Beat in oil, pumpkin puree, egg, and vanilla. Gradually add flour mixture and beat just until incorporated.
Shape dough with a medium cookies scoop and place 2 inches apart on prepared cookie sheets. Gently flatten cookies with the bottom of a glass dipped in granulated sugar.
Bake in preheated oven 9-12 minutes or until centers are set. Cookies will not brown, do not overbake.
Remove baking sheets to a wire rack and let cookies cool on sheets 3-5 minutes. Gently transfer cookies directly onto wire racks and cool completely.