Line a 9 x 9-inch pan or baking dish with heavy duty aluminum foil leaving enough overhang to remove from the pan. Spray lightly with cooking spray.
In a large mixing bowl, use a mixer to beat together 1 1/4 cup peanut butter, 1 cup powdered sugar, 1 1/2 sticks softened butter and vanilla until smooth.
By hand mix in 3 cup chopped pretzels, 1 cup powdered sugar and 1/2 cup chocolate chips. Stir until fully moistened. Press peanut butter pretzel mixture evenly into the pan.
In a microwave safe bowl, melt the remaining chocolate chips and 3/4 cup peanut butter in 30-second intervals. Repeat stirring until completely smooth. Pour over the pretzel bars and spread evenly.
Sprinkle the top with the remaining 1/2 cup broken pretzels and chopped peanuts. Refrigerate for at least 4 hours to set. You can freeze to speed up the process.
Use foil to lift from pan. Use a sharp knife to cut into squares and serve. Store chilled for up to 5 days.