In a medium-sized bowl, whisk together the all-purpose flour, baking soda, cornstarch, and salt. Set it aside.
2
In a large mixing bowl, cream together the softened unsalted butter, sugar, light brown sugar, and dark brown sugar using an electric mixer on medium speed.
3
Add in the large egg and pure vanilla extract, mixing until fully combined.
4
Mix in the pumpkin puree, pumpkin pie spice, and ground cinnamon until thoroughly incorporated.
5
Gradually add the dry ingredients into the wet ingredients, mixing until a thick and sticky dough is formed.
6
Gently fold in the butterscotch chips until evenly distributed.
7
Cover the dough and freeze for at least 2 hours or overnight.
8
Preheat the oven to 350°F (175°C) when ready to bake the cookies. Allow the cookie dough to thaw for about 10 minutes.
9
Using a cookie dough scoop or spoon, scoop 1.5 tablespoon-sized balls onto a parchment-lined baking sheet, spacing them apart.
10
Press a few additional butterscotch chips onto the tops of each dough ball, if desired.
11
Bake the cookies for 10 minutes, then allow them to cool on the baking sheet for 15-20 minutes before transferring to a wire rack or serving plate.