Line a 9x13" pan with foil or waxed paper. Spray with cooking spray.
Use a food processor to crush 11 ounces of pretzels. Remove the blade and shake the bowl. The larger pieces will rise to the top. Scoop off 1/2 cup of the larger pieces and set them aside.
Melt the butter in a large microwave-safe bowl. Add the peanut butter, powdered sugar, and vanilla. Beat with a hand mixer until smooth, then stir in the pretzel crumbs.
Spread the peanut butter mixture into the prepared pan. (An offset spatula works great!)
Stir together the 1/3 cup of peanut butter and chocolate chips in a glass bowl. Cook at half power in the microwave, stirring every 30 seconds until melted.
Spread the melted chocolate over the bars. Sprinkle the 1/2 cup of crushed pretzels and peanuts over the top. Gently press them into the chocolate topping.
Cover and chill for at least an hour, or until the chocolate sets up.
Remove from the pan and use a sharp knife to cut into squares.
Notes
You can store leftover bars in the refrigerator for up to a week in an airtight container or wrapped individually in plastic wrap.