In a medium bowl, combine flour, baking soda, cornstarch, cinnamon, pie spice, and salt. Set aside.
In the bowl of a stand mixer fitted with a paddle, combine butter and sugars, mixing on medium speed for 2 minutes. Add in egg white and vanilla and mix until incorporated, then follow with the pumpkin puree.
Gradually add the dry ingredients into the wet, mixing until smooth.
On low speed, add in the butterscotch chips, only mixing until uniform.
Refrigerate the dough for 30 minutes to 24 hours.
Combine ingredients for streusel topping in a small bowl and cut together with the prongs of a fork until evenly crumbly.
Line your baking sheets with parchment of Silpat liners.Preheat oven to 350 degrees F.
Using a medium cookie scoop, scoop dough on to prepared baking sheets, leaving about 2 inches between each cookie.
Sprinkle streusel topping generously on each cookie.
Bake for 8-10 minutes, until bottoms are barely browning and tops no longer look wet.
Remove from oven and cool cookies on baking sheet for 5 minutes, before moving them to a cooling rack to finish cooling.