Place the pumpkin puree in a small bowl and blot it down with several paper towels to remove excess moisture. You will be surprised how much water gets absorbed! Measure out 1/2 cup of pumpkin puree and set aside.
In a large bowl, whisk together the melted butter, sugars and vanilla until smooth. Add in the pumpkin puree and egg- whisk until no lumps remain.
In a medium bowl, whisk together the flour, salt, baking soda, baking powder, pumpkin pie spice, cinnamon and corn starch. Add the wet ingredients to the dry ingredients and stir by hand until cookie dough is formed. Cover with plastic wrap and place in the refrigerator to chill for at least 30 minutes or up to 3 days.
When ready to bake cookies, preheat oven to 350 degrees F and line two baking sheets with parchment paper or silpat mats. In a shallow dish or small bowl, combine the granulated sugar and cinnamon together.
Use a small ice cream scoop, or portioning out 2 tablespoons of cookie dough per cookie. Roll into a ball and then roll into the cinnamon sugar mixture to coat the entire dough ball. Arrange cookies on the baking sheets and press down on the cookie with your hand as the cookies will only spread a tiny bit when baking.
Bake the cookies for 9-10 minutes. They will seem under baked but they will cook more as they cool. Place the baking sheets on a wire rack or cool surface to cool for a few minutes. Then remove the cookies from the baking sheet and place on wire rack to cool completely. Enjoy!