Place the softened butter into a large mixing bowl along with the canola oil, granulated sugar, and brown sugar. Cream together using an electric mixer.
Add the egg, pumpkin puree, and the vanilla. Beat well.
In a separate bowl, mix the flour, cream of tartar, baking soda, salt, and the pumpkin pie spice.
Add the flour mixture to the pumpkin and sugar mixture. Stir until combined.
Place the dough in the refrigerator for 10 to 15 minutes before continuing.
Mix ¼ cup granulated sugar with the pumpkin pie spice or cinnamon in a bowl large enough to roll cookie dough balls in.
Scoop out the cookie dough using a spoon or cookie dough scoop, and roll it into balls. Coat the cookie dough in the spiced sugar mixture and place on a cookie sheet at least 2 inches apart.
Use a drinking glass, or something with a flat bottom, to lightly flatten the cookie dough. Dipping the glass into the dough and then the spiced sugar mixture helps prevent the glass from sticking to the cookies.
Bake cookies in a 350-degree oven for 12-15 minutes. Cool slightly on the cookie sheet, then move cookies to rack to cool completely.
Makes about 4 dozen cookies.
By baking the Pumpkin Snickerdoodles for 12 minutes gives you a very soft cookie. Baking them for 15 minutes results in a crisper cookie. You could try to bake for a minute or two more for a slightly crunchy cookie.