Active time: 2 hours
Make the bars:
Line an 8" square baking pan with foil, leaving a 2" overhang on all sides; lightly coat the foil with cooking spray. In a medium bowl, whisk together the flour, baking powder and salt.
In the bowl of a stand mixer fitted with a paddle attachment, or in a bowl with a hand-held mixer, beat the peanut butter, butter and sugars at medium speed until well blended. Add the egg and vanilla extract and continue to beat until well blended. Gradually add the dry ingredients and beat on low speed until just combined.
Press about half of the dough evenly into the bottom of the prepared baking pan. Transfer the remaining dough to the freezer and let chill for at least 10 minutes. Spread the cranberry sauce in an even layer over the dough. Remove dough from the freezer, squeeze off chunks and sprinkle over the cranberry sauce. Sprinkle the peanuts on top. Transfer to the freezer to chill for at least 30 minutes.
Preheat oven to 350 degrees with rack in center position. Bake bars until the top is lightly golden, 30-40 minutes. Remove pan from the oven and let cool completely. Using the foil overhang, lift bars from pan and transfer to a cutting board. Cut into 16, 2 inch squares.