I made a graham cracker crust just like I would for a cheesecake, pressed it into the bottom of my pan, and blind baked it. Once that came out I added the brownie mix (mixed according to package directions, I like the fudgy kind) and baked again until the brownie was done. For the finishing touch, I added a layer of mini-marshmallows on top and put the whole thing under the broiler for a few moments to toast 'em up. The result is delicious!! It is reminiscent of a S'More but it isn't an exact taste replica, almost like a grown-up S'More. I highly suggest that you mix up a batch today. To make slicing easier you can spray a little Pam on your knife before you dig in, it'll help with the marshmallow layer.
In case you need it, here's what I used to make my graham cracker crust:
1 1/2 Cups crushed graham crackers
6 TBSP Melted butter
1 TBSP Sugar
A Pinch of salt
Mix it all together in a bowl or food processor until graham crackers and butter are completely combined. Use a large spoon (or your hands) to press crust mixture into bottom of baking dish. Bake at 325 for 10-15 minutes or until it is a buttery golden brown.