I have made black bean brownies. My kids didn't taste the difference. I have to be careful when I made them, because it's easy to just up the beans and give myself license to eat way too many.
I have seen recipes for cookies with white beans or garbanzo beans. I remember they said peanut butter cookies work well to mask the flavor, along with the beans adding protein.
On an unrelated note, I also made tofu mac and cheese once for my kids. I don't think I ever told them what was different. They told me it was the best ever. It did have lots of cheese, but I didn't need to add as much cheese as I normally would because the tofu is like a cottage cheese. Plus, the extra protein fills you up faster. I had heard of tofu used that way before, but I didn't believe it would be as tasty. It's really good as long as the tofu base is seasoned.
