Preheat the oven to 350°F. Line a 9-inch baking pan with parchment paper and set aside.
In a medium bowl, whisk together the gluten free all-purpose flour, cocoa powder, black cocoa powder, and salt. Add the sugar, butter, and eggs, and whisk until combined. Stir in the coffee liqueur, vanilla extract, and espresso powder.
Spread the brownie batter evenly into the prepared pan, and bake for 22-25 minutes, or until JUST set. (NOTE: for a cakey brownie, bake for 4 minutes longer.
Remove the pan from the oven and let cool for 8-10 minutes. Place brownies in the refrigerator on a cooling rack, and cool for another 15 minutes. Meanwhile, make the glaze.
For the glaze, stir the espresso powder into the hot water. In a medium bowl, whisk together the powdered sugar, cocoa powder, and black cocoa powder. Add the espresso mixture, butter, coffee liqueur, and salt. Whisk until combined.
Remove the brownies from the refrigerator and spread glaze evenly over the top. Return to the refrigerator, and let cool completely. Cut into 16 equal squares before serving. ENJOY!