In a large mixing bowl or stand mixer, add the chunks of cold butter (make sure it's cold) and brown sugar. Mix for 3 minutes, or until the butter and sugar are well combined, lighter, and fluffy.
Add the pumpkin puree, egg, sour cream, and vanilla. Mix just until everything is combined.
Add the flour, pumpkin pie spice, baking soda, cream of tartar, and salt. Mix until the dry ingredients are incorporated, just until it becomes a dough.
Chill the dough for 30 minutes in the fridge.
When the dough is almost done chilling, preheat the oven to 350.
Using a 2 inch cookie dough scoop, get a ball of dough and flatten it in your hand. Place a piece of chocolate (if you are adding chocolate) in the middle of the dough and close the rest of the dough around it. Roll it in your hands until it forms a smooth ball. Repeat with the remaining dough.
In a small bowl, mix the cinnamon and sugar together. Roll each dough ball in the cinnamon and sugar until it is all covered.
Place 12 cookies on a baking sheet and bake for 10-12 minutes. Let the cookies cool completely before eating. Enjoy!
