In a large bowl, whisk together the flour, brown sugar, granulated sugar, baking soda, baking powder, salt and pumpkin pie spice. In a medium bowl, whisk together the pumpkin puree, buttermilk, egg, and molasses. Coat the cold butter block with additional flour to allow for easy holding. Use the largest holes of a box grater, shred the cold butter into the flour mixture and stir with a fork just until combined. Add the pumpkin puree mixture to the flour mixture and add the butterscotch chips. Stir with a wooden spoon just to combine.