Mash the sweet potato and mix with oat flour, cacao powder, vanilla, maple syrup, and salt until a thick brownie dough forms. Press into a lined container or tray.
Blend dates, peanut butter powder, salt, and a little water until smooth and caramel-like. Spread over the brownie layer.
Top with melted vegan dark chocolate if using, then chill until firm before slicing.
