So the recipe comes out of 50 Bar Cookie Recipes insert , and available online (at least at the time of this post) and can be found here. You will have to scroll through the different bar recipes to find the triple decker recipe. However, the recipe will tell you make the classic brownie recipe and the classic blonde layer. So you have to look at three separate recipes to make this one.
So if some point in the future if the link goes away, it is just a brownie layer, an Oreo layer, and a blondie layer. Bake at 350 degrees until a toothpick comes out clean.