Make the chocolate covered pretzels first. In a medium bowl, break up and melt the 2 oz of chocolate in the microwave. Toss the broken pretzels into the melted chocolate and stir around until they are covered. Put on parchment paper on baking sheet and refrigerate.
Melt butter and semi-sweet chocolate in a medium saucepan on medium heat, stirring constantly, about 6 minutes. Remove from heat and let cool to room temperature. About 15 minutes. Preheat oven to 350º.
Stir sugar into cooled chocolate butter mixture until combined. Add in the eggs one at a time, whisking until smooth after each addition. Whisk in the vanilla. Gently fold in the flour and salt. Spray an 8×8 pan with cooking spray. Pour batter into prepared pan, smoothing the top with a knife. Bake for 30-35 minutes until a toothpick comes out almost clean, don’t cook too much.
Using an electric handheld mixer, cream the butter and peanut butter on medium speed until completely smooth and no more chunks of butter are visible. Slowly mix in confectioners sugar, starting with just one cup. Add more confectioners sugar as needed. You want a very thick frosting layer.
Once the brownies are completely cooled about 1 hour, frost with peanut better frosting. Chop up your chocolate covered pretzels and layer them on top of the frosting, gently pressing them down so that they stick. Refrigerate brownies for 30-60 minutes until the frosting sets on top of the brownies. Cut into squares and keep refrigerated.