Preheat the oven to 350 degrees and line an 8 x 8 pan with parchment paper leaving an overhang on 2 sides or spray the pan with cooking spray.
Combine butter and chocolate in a medium saucepan over low heat until melted, stirring often.
Add the espresso powder and sugar and stir to combine.
Add the eggs and stir until combined.
Add the cocoa powder, flour and salt and stir until there are just barely streaks of flour remaining.
Pour the batter into the prepared pan, smoothing the top and bake for 25-30 minutes until set in the middle and done on the sides and a toothpick inserted contains moist crumbs.
Transfer to a wire rack to cool completely in the pan. Once cooled remove the brownies from the pan (if you used parchment paper) and frost with the espresso frosting. Sprinkle with chopped chocolate covered espresso beans if desired.
In a medium bowl (or using a stand mixer), mix the butter with an electric mixer until creamy.
Add the powdered sugar and mix until combined.
In a small bowl, combine the espresso powder and milk and stir until the espresso powder is dissolved.
Add the espresso mixture and vanilla to the frosting and mix until light and fluff