Preheat oven to 350 degrees. Grease an 8 x 8 inch square baking dish. Combine the black beans, eggs, oil, cocoa powder, salt, vanilla and sugar in the blender. Blend until smooth. Pour the mixture into the prepared baking dish. Sprinkle chocolate chips on top of the batter or mix gently in swirls into the batter. Bake in oven until the top is dry and edges start to pull away from the sides of the pan. When done, remove from oven, frost with your favorite frosting while still warm.