Pre-heat oven to 350 degrees. Line an 9"9" baking pan with foil and lightly butter.
In a medium bowl, whisk together flour, baking powder, pumpkin pie spice, and salt.
In the bowl of a mixer (or in a regular large bowl with a hand mixer), beat together butter, pumpkin puree, brown sugar, and granulated sugar for about 2-3 minutes. Add eggs and vanilla and beat until combined, about 2 minutes.
Add in flour mixture and mix until just combined and batter is smooth.
Pour batter into prepared pan and smooth. Bake for 25 minutes. Remove from oven and sprinkle mini marshmallows and butterscotch chips over the top. Bake for another 8-10 minutes, until marshmallows are getting toasty.
Let cool before removing from pan and slicing into bars.