Lightly grease a square 8x8 or 9x9 inch baking pan with oil or butter. Line with parchment paper. Preheat the oven to 350 degrees F (177 C).
In a glass bowl, heat the butter in the microwave for 25 seconds until softened/partially melted. Add the chocolate and heat in the microwave for 20 seconds. Give it a good stir. If there are still chocolate chunks, microwave for 15 seconds then stir and repeat as necessary until a silky melted mixture forms (do not over-microwave, it will burn the chocolate and create a nasty paste).
In a separate bowl, whisk the eggs and brown sugar together quite vigorously for 1-2 minutes until frothy (you can also use an electric hand mixer and mix until bubbly and slightly lightened in color). Add the melted chocolate mixture and mix until combined. Sift in the salt, cocoa powder, espresso powder, baking powder, and GF flour and whisk until mostly combined. Add the vanilla and whisk until everything is well incorporated. If you would like to, fold your desired amount of additional chocolate chips into the batter.
Pour the batter into the prepared pan and bake for about 20 minutes for the best fudgy texture. Remove from the oven and let it cool until just warm before serving. Serving directly out of the oven would be a molten mess, but I personally don't mind as long as there are plates and spoons nearby! Allowing the brownies to cool will give them more structure. Enjoy!
