1Whisk together flour, cornstarch, baking soda, baking powder, salt, and spices; set aside.
2Have the mixer fitted with paddle attachment, cream butter and sugars together, just till combined. Occasionally scrape down sides and bottom of bowl through out mixing process -- if you are not using a paddle attachment.
3Mix in egg yolk, then pumpkin and vanilla. On low speed, slowly add in dry ingredients, mix until combined. Divide dough in half and place each half in a bowl, cover with plastic and chill 45 minutes to an hour. The dough should be slightly sticky so the cinnamon sugar will stick when rolling, but they should be manageable to roll in the palms of your hands.
4Preheat oven 350, during the last 10 minutes of refrigerating the dough.
5In a small bowl whisk together sugar with cinnamon for rolling.
6Scoop dough out 2 level TBS at a time; shape into a ball, roll dough ball in cinnamon sugar mixture to evenly coat; transfer to parchment lined baking sheet, spacing 2" apart. Bake 12-14 minutes, they should look just slightly under cooked, they will continue cooking slightly when cooling on the baking sheet. Cool on baking sheet 5 minutes; transfer to wire rack to cool completely.