Make the brownie batter first. Start by adding the aquafaba to a large mixing bowl. and whisk it until bubbles form.
Add in the sugar and continue whisking for another minute until a thin paste forms.
Melt the chocolate in a microwave. Add the peanut butter, melted chocolate, milk, and vanilla extract and stir until combined.
Add the cocoa powder, flour, and salt then stir to combine just until no more dry flour is visible. Transfer the brownie batter to a prepared baking pan and smooth out to create an even layer. Set aside.
Make the blondie batter next. Add the aquafaba, sugar, peanut butter, and vanilla to a second large mixing bowl. Stir well to combine.
Add the flour, baking powder and salt and stir until just combined. Then fold in the chocolate chunks. The batter will be thicker, more like cookie dough consistency.
Add the blondie batter to the pan on top of the brownie batter and spread out. Swirl the two together if desired. Bake on the center rack for 40-45 minutes at 350F.
Allow to cool in the pan for 10-15 minutes before slicing. I know it's hard to resist, but they continue to set as they cool. If you slice into them too soon they may be too gooey.