Line an 8x8 baking pan with parchment paper (wax paper and aluminum foil works too). Set aside.
Crush pretzels into fine crumbs using a food processor. Place pretzel crumbs, peanut butter, butter and confectioners sugar in a large bowl of a stand mixer.1 Mix on medium speed until well combined.
Transfer mixture to prepared pan and spread evenly using a rubber spatula or knife. Prepare melted chocolate.
Place chocolate chips and shortening in a microwave safe bowl. Heat for 1 minute on 50% power level. Stir and heat in 30 second intervals at 50% power level. Continue until chocolate is smooth and melted.
Pour melted chocolate over pretzel mixture and spread evenly. Place mini pretzels on top for garnish.
Place bars in the refrigerator to chill for at least an hour. When set, remove the bars from pan, cut and serve.
You can also use a hand mixer or stir vigorously by hand for this recipe.
Store peanut butter pretzel bars in an airtight container in the fridge for up to a week. They be kept at room temperature when serving if desired.
Peanut butter pretzel bars may be frozen for up to a month. Store bars between layers of parchment paper in an airtight container in the freezer.