Preheat oven to 350° and adjust oven rack to middle position.
Spray an 8 or 9 inch cast iron skillet, cake pan, or casserole dish with nonstick spray.
Using either a food processor a plastic storage bag and rolling pin, crush graham crackers into a fine crumb. Mix with melted butter, brown sugar, and salt until combined. Press into bottom of prepared baking dish and bake for 8 minutes. Prepare brownie batter while crust is baking
In either the microwave or a small pot on the stove, melt together chopped chocolate and butter. Do so over low heat to ensure not to burn the chocolate. If using a microwave stop in 30 second intervals to stir. Set aside.
Using either a hand or stand mixer with paddle attachment, in a mixing bowl add eggs, sugars, and vanilla. Mix on medium speed for 2-3 minutes. This is an important step in achieving crackly topped brownies. Add in melted chocolate and butter mixture and mix until combined.
Add salt, all purpose flour, and cocoa powder to bowl. Mix until just combined. Mixture will be thick. Be careful not to over mix. Add in chocolate chips and mix until just combined.
Pour batter on top of pre baked graham cracker crust and smooth to edges of pan. Bake in preheated 350° oven for 25-35 minutes. 25 minutes will produce a fudgier, gooey brownie. 30-35 minutes will produce a chewier brownie. Set aside and turn oven temperature up to broil.
Top brownie skillet with marshmallows. Stick back in oven once it has reached broiling temperature to toast marshmallows. Broil for 2-5 minutes, keeping a close eye on marshmallows to avoid burning. Once marshmallows are toasted remove from oven and set aside. Let cool for five minutes.
Top brownie skillet with any combination of graham crackers, graham cracker crumbs, and milk chocolate. Enjoy!