Heat oven to 350°F. Line a 9x9 square baking pan with two small, overlapping sheets of parchment paper. Set aside.

Place the butter and chocolate chips in a medium, microwave-safe bowl, and heat in 30-second increments until the butter has completely melted. Add the cocoa powder and instant espresso powder, and stir until smooth.

In a separate large bowl, beat the sugar and eggs with a mixer until pale yellow. Pour in the butter and chocolate mixture and mix until combined. Fold in the flour, salt, and vanilla extract until just combined. The batter will be thick.

Pour the brownie batter into the parchment-lined pan, spread it out evenly, and bake for 30-35 minutes, or until a toothpick poked in the edges comes out clean. Let the brownies cool completely on a wire rack.

Once the brownies have cooled, stir the espresso powder and water together in a small bowl until the espresso powder has dissolved. Set aside.

In a large mixing bowl, cream the butter until smooth, then gradually mix in the powdered sugar. After you’ve added about 2 cups of the powdered sugar, pour in the espresso, vanilla extract, and salt. Continue adding the remaining powdered sugar until the frosting is thick and smooth.

Spoon the frosting on top of the cooled brownies and smooth it out evenly. Slice the brownies, and serve at room temperature.