Blondies or brownies?
It's a delicious dilemma: they're both bar cookie classics, one rich in brown sugar, the other redolent of chocolate.
But why should you have to decide? Because they taste so much better when baked together, in layers.
How'd I do it? Well, since brownies generally have a longer bake time, I started out my pan with a batch of brownie batter which I put in the oven for 20 minutes while I put together the blondie batter. Since the half-baked brownies would have gotten messy had I spread the blondie batter on top, I simply spooned the batter as gently as I could right on top and put it back in the oven for about 25 more minutes; the oven's heat did a nice job of spreading the batter for a tasty two-layered treat. 
For the full entry and recipe, visit Serious Eats!