The black bean brownie is an American variation that uses bean puree as the base of the batter. This gluten-free recipe is based on a simple idea: replacing flour with a natural ingredient rich in protein. The result is a dense, moist, and structured cake, and the cocoa gives it the sweetness that children crave. It's a dessert designed for simplicity, to be prepared with everyday ingredients. The mixture is made in a blender or food processor, to obtain a smooth batter effortlessly. This gives the characteristic texture of a brownie without using traditional flour. As with the traditional brownie, you can add nuts. This cake is delicious, but be careful not to overbake it or it will become dry.