In a small bowl, combine flour, baking powder, pumpkin pie spice, and salt; set aside.
In a large bowl, cream together the butter and brown sugar. Add the eggs and vanilla extract, and beat until well combined.
Add the flour mixture and stir just until combined.Fold in the chopped cranberries and white chocolate chips.
Spread the batter evenly into the prepared baking dish. Bake for 20–30 minutes until the bars are lightly brown on top.
Allow to cool completely. and then frost.