Preheat oven to 350F. Line an 8 x 8 inch baking dish with foil and spray with cooking spray. Set aside.

In a blender or food processor puree the black beans and milk until smooth then add the rest of the ingredients except the peanut butter, ending with dry ingredients. Mix until smooth and combined then pour into the prepared baking dish. Set aside.

Melt the peanut butter in a microwave-safe bowl. Spoon the melted peanut butter on top of the batter and swirl with a knife to create a marbled look. Place the brownies into the preheated oven for 20 to 30 minutes or until the outside of the brownies pulls away from the dish and a toothpick inserted in the center comes out clean.

Allow the brownies to cool completely before cutting into squares.