Mix the aquafaba and sugar. Add the aquafaba and sugar to a bowl. Use a handheld or standing mixer to beat the two together. You’ll know it’s done when the mixture looks thick, glossy, and has wavy ribbons. Now you can fold the vanilla, salt, and espresso powder into the aquafaba mixture.
Melt the chocolate. Place a heatproof bowl on top of a saucepan filled with a few inches of water. Place the chopped chocolate and vegan butter in the bowl and heat the water until it’s at a rapid simmer. Stir until the chocolate has melted.a
Fold the melted chocolate mixture into the aquafaba mixture until well combined. Finish the batter. Gently stir the dry mixture into the wet ingredients until just combined and no dry flour remains. Fold in the chocolate chips.
Transfer the batter into your lined 8×8-inch (20×20 cm) baking pan and smooth out the surface with a spatula. Bake. Bake the brownies for 34 to 37 minutes until a toothpick inserted in the middle comes out with some moist crumbs.