Heat oven to 350°F. Lightly grease an 8x8-inch baking pan with ghee or line it with parchment paper.
Measure out ½ cup of aquafaba (the liquid from a cans of chickpeas). In a medium mixing bowl, use a hand mixer to whip the aquafaba until it becomes thick and foamy, about one minute.
Stir the coconut sugar, date syrup, espresso granules, baking soda and salt into the aquafaba. Stir gently, then set the bowl aside so the coconut sugar has time to begin dissolving.
Break the chocolate bars into small pieces and place them in a heat-safe bowl with the ghee. You can melt this mixture in the microwave, heating in 30-second intervals and stirring between each, or use a double boiler on the stovetop. If you choose a double boiler, set the bowl over a saucepan with about an inch of simmering water—just be sure the bottom of the bowl doesn’t touch the water. Stir until the chocolate and ghee are fully melted, combined, and smooth. The melted mixture will be quite thin.
While still hot, pour the chocolate mixture into the aquafaba mixture and whisk well. The warm chocolate will begin to thicken.
Fold in the garbanzo bean flour. The finished batter will be thick and glossy, but still easy to pour.
Transfer the batter into the prepared baking pan. Sprinkle the top with flaky sea salt, if desired.
Bake for 30 to 35 minutes, or until a toothpick or cake tester inserted in the center comes out clean.
Let the brownies cool completely before cutting into squares.