I haven't made my own from scratch yet, something I'll get to trying one day.
I have done the mix a can of black beans with boxed brownie mix thing though and it comes out delicious! I can't taste the black beans, and it's more fudgey than mixing with oil and eggs. Not sure if this is really any healthier though, since it's definitely not something I can have in the house cause I'll just keep eating them! I just dump the whole can of black beans, liquid and all, with a box of brownie mix and blend it all together (blender, food processor or handmixer) and bake!