Preheat your oven to 350°F and grease a 13"x9" metal baking pan with cooking spray. Line it with parchment paper, leaving some overhang on two sides, and grease the parchment too.
In a large bowl, use an electric mixer to beat together the brown sugar, melted butter, peanut butter, baking powder, vanilla, and salt until combined. Add the eggs one at a time, beating well after each addition.
Fold in the flour until just combined, then gently mix in 2 cups of pretzels (lightly crushed) and 2/3 cup of butterscotch chips.
Spread the batter into the prepared pan, then press the remaining 1/2 cup of pretzels on top. Sprinkle with the remaining 1/3 cup of butterscotch chips.
Bake for 23 to 27 minutes, or until golden brown and a toothpick inserted into the center comes out clean.
Let them cool completely before using the parchment overhang to lift them out of the pan and cutting them into squares. Enjoy your delicious peanut butter blondies!