The recipe for black bean brownies is from FarmBoy. It is very simple and is gluten free as well. WRT baking, I ended up extending the baking time to be 23 minutes as we are sea level and it takes a bit longer.
As for the taste. Well now. I found them a bit chalky. Otherwise they are pretty much like any other brownie. I would say you want to make sure that the beans are emulsified very very smoothly. I noticed that we had a few hunks of skin from the beans that weren't fine enough that you could taste on your tongue as you were eating them. I didn't bother with icing for these but I think powdered sugar would be nice as a topper. Eating them a little warm certainly brought out the flavor of the chili. I wonder if the chili flavor will be stronger if they are cold? And the answer to the question is no, it is not.