I got the recipe from Chocolate-Covered Katie's blog. It's called Giant Chocolate-Chip Cookie Cake. It's vegan, but you won't realize it. It's also healthy, but you won't realize that either. I took it to a brunch today and no one said to me "You know, Tina, this cookie cake tastes healthy and beany."
Here's my two cents on the making of the recipe itself. I used cannelloni/white beans, just a normal size can. I did not pack the brown sugar. I cooked it for 25 minutes and it could cook longer, but it won't ever get dry like a normal cookie, it will always be dense.
I stored it over night once and it was okay the next day, but not nearly as good as the first. You do not want to put plastic wrap over it as it's super moist and throws off a lot of moisture even after baking. I used milk chocolate chips which were super tasty. It smelled good, looked good and tasted good. And it does not take very long to put together and you can keep the ingredients on hand for a quick dessert.