Place pretzel sticks n the bowl of a food processor and pulse until finely crushed. (If you don't have a food processor, place pretzels in a gallon sized plastic bag and crush with a rolling pin). Add melted butter and pulse to combine.
Using fingers or spatula, press crumbs evenly into bottom of a 9 x 13-inch baking dish. Bake at 400 degrees for 8-10 minutes, or until crust is lightly browned.
Remove from oven and place baking dish on a wire rack to cool slightly.
In a large bowl, use a spoon to combine peanut butter, butter, powdered sugar, and vanilla. Mix until well incorporated. Use spatula to spread evenly on top of pretzel crust.
Sprinkle 4 ounces of crushed pretzels evenly over peanut butter filling.
Place chocolate chips and shortening into a microwave-safe bowl. Heat on high for 45 seconds. Stir and heat on high for another 45 seconds. Stir until chips are melted. Use spatula to spread chocolate evenly over pretzels.
Chill bars in refrigerator for at least 60 minutes before slicing and serving.