Preheat oven to 350 degrees F. Grease and flour an 8×8 baking dish and set aside.
Combine melted butter and pretzel crumbs in a bowl until moistened. With the back of a spoon, press pretzels into the 8×8 pan making a crust. If pretzels seem loose, drizzle some additional melted butter over top of hit with a quick shot of non-stick spray.
In the bowl of an electric mixer, beat butter and sugar until fluffy. Add eggs one at a time, then add vanilla. With the mixer on medium speed, add in cocoa, flour and salt, mixing until combined – about 2 to 3 minutes. Fold in chocolate chips. Using a spatula sprayed with non-stick spray, evenly spread brownies on top of pretzel crust. Set pan on a baking sheet and bake for 25-30 minutes, or until brownies are baked through.
When brownies have about 3 minutes left baking, melt peanut butter (I melted mine in the microwave in 30 second increments then stirring) in a bowl. Once melted, stir in 1/3 cup powdered sugar and mix until no lumps remain. Pour over warm brownies and spread evenly. Refrigerate brownies for 1-2 hours, then cut into bars and serve.