Pre-heat your oven to 350º Fahrenheit.
In a medium sized mixing bowl, add cocoa powder, flour, baking powder.
Use a whisk to gently mix together until fully incorporated.
In a larger mixing bowl, add the aquafaba and the sugar.
Use an electric beater and beat on medium until the mixture becomes thick and glossy, about 3 minutes.
Heat a pot of water until simmering and place a heat-safe mixing bowl over the pot to create a double broiler.
Add the vegan butter and chopped chocolate bar (not the chocolate chips), and stir until melted. Remove from heat and set aside.
Once the aquafaba mixture is thick, add the vanilla, the cooled chocolate butter mixture, and non-dairy milk.
Gently fold until combined.
Sift the dry ingredient mixture into the aquafaba mixture and stir until a thick batter is formed.
Add chocolate chips if desired, stir to combine.
Line a 8 x 8 inch baking pan with parchment paper.
Gently pour in the brownie batter and spread the top so that the batter is even.
Bake in the oven at 350º F for 35-42 minutes, or until a toothpick comes out mostly clean.
Allow the brownies to cool completely. If the center feels very soft, I recommend letting in cool in the fridge until completely solid.
Slice into 9 pieces and enjoy!