Add the dry ingredients to a large mixing bowl. Whisk them together until evenly combined. Set aside.
To the bowl of a stand mixer, add the butter & sugar. Whip together until smooth & creamy.
Add the egg yolk and vanilla extract to the mixing bowl, whip again until completely incorporated.
Add the pumpkin puree to the bowl, and mix again- just until combined.
Set your mixer on low speed, and slowly add in the flour mixture. Continue mixing until the batter has come together. Using a spatula, scrape down the sides of the bowl and the center and mix again.
Remove the mixing bowl from the mixer, and cover it tightly with plastic wrap. Chill it in the refrigerator for 30 minutes.
Line a large baking sheet with parchment paper. Add some extra sugar to a small prep bowl, and set aside.
Using a medium sized scoop, roll a scoop of dough in between the palms of your hands until it's a roughly smooth 1 inch ball. Roll it in the sugar and then place it on the prepared baking sheet.
Continue, placing the cookie dough balls about 2 inches apart until all the dough has been used- or your baking sheet's full.
Bake at 350° for 20 minutes.
Carefully remove the hot cookies from the oven, and let them rest on the pan for 5 minutes.
Transfer the cookies to a waiting cooling rack to finish cooling completely.