I read a book by Mallery this summer (among many :)) with a recipe in the front. It was DIY mint Brownies. It was short, but not quite as sweet as I thought. I have a link to the recipe that someone "borrowed" (I'm being nice) from the book here. I followed the directions and put the cookies right into the mix. The brownies didn't cook all the way so they were extremely gooey and bordering on dough.
I tried again. Maybe if the cookies were on top then the brownies would cook all the way. I gave them five extra minutes and they were still really gooey - like not done at all. So I stuck the brownies back in the oven and ended up with too done.
I think there were several factors that made this difficult. One, the brownie mix was superior and required that the brownies cook for the specific amount of time to get perfection. We've cooked these following the directions and always get the best result. Two, the cookies were inferior. Cheapy chocolate with little mint. Nice to eat by themselves, but not good for this recipe. Three, we think the recipe was too vague.
I love using premade stuff and mixing it with homemade to get unique baked goods, but this one missed the boat.