Preheat oven to 350°F (177°C). Lightly grease a 9x13-inch pan.
In the bowl of a stand mixer, beat eggs at medium speed with the cocoa, salt, baking powder, coffee and vanilla for 4 minutes. Meanwhile, melt the butter.
In a saucepan over low heat, melt the butter. Add the sugar and stir to combine. Heat through until the mixture is hot (about 110°F to 120°F) but not bubbling. It will appear shiny. Turn off the heat
Slowly add the butter and sugar mixture to the egg mixture, stirring until smooth. Then add the flour and chocolate chips, stirring until fully combined.
Transfer the batter to the prepared pan. Bake for 30 minutes or until a toothpick or cake tester inserted into the center comes out clean. Remove from the oven and allow to cool completely.
Make the peanut butter frosting.
In a microwave safe bowl, heat peanut butter and butter in the microwave in 20-second intervals until smooth. Stir in powdered sugar and vanilla until combined.
Spread the frosting evenly over the brownies.
Make the pretzel topping.
Put the pretzels in a plastic bag. Beat with a wooden spoon or potato masher until broken into 1-inch pieces. As best you can, separate the larger pieces from the crumbs.
In a microwave safe bowl, heat chocolate chips in the microwave in 20-second intervals until melted smooth, stirring in between. Stir in the pretzels.
Spread the topping evenly over the brownies.
Finish the brownies.
Place the brownies in the fridge for 30 minutes to allow the layers to firm up. Once firm, cut into 4-inch squares. Serve!