Specifically, it consists of chocolate brownie batter spread out and placed atop chocolate chip cookie dough and then baked together.
You can find it at Papa John's for $6.
The name brings to mind the fey inhabitant of a river or the like rather than something I'd want to put in my mouth, but that's just me. Domino's introduced a similar option earlier this year; they call it the "Marbled Cookie Brownie."
The pizza chain is also offering a deal where you can get a large, one-topping pizza for 50 cents, when you buy any large pizza at regular menu price.
Nutritional Info - Papa John's Brookie
Serving Size - 1 slice - 1/8th of Brookie (41g)
Calories - 190 (from Fat - 80)
Fat - 9g (Saturated Fat - 4g)
Sodium - 95mg
Carbs - 26g (Sugar - 17g)
Protein - 2g