2Line bottom and sides of a 9x13 inch baking pan with foil, leaving an overhang on the sides.
3In a medium bowl, whisk the first 4 ingredients together. Set aside.
4With an electric mixer, cream butter and sugar on medium high speed until smooth, beat in egg and vanilla until combined.
5Beat in pumpkin puree (don't worry if it looks curdley). Reduce speed to low and mix dry ingredients until just combined. Fold in butterscotch chips.
6Spread batter evenly in prepared pan. Bake until edges begin to pull away from side of pan and a toothpick inserted in center comes out with just a few moist crumbs, attached, 35-40 minutes. Cool completely in pan.
7Lift bars from pans (using the foil to help). Peel off foil, and use a serrated knife to cut into 24 squares.