Mix melted butter, sugar, and graham cracker crumbs until well combined.
Press into a parchment-lined 8 x 8 baking dish.
Bake for 5 minutes.
Brownies
Whisk eggs and sugar until light and airy.* Set aside.
In a separate bowl, combine melted butter and chocolate and mix until smooth. You may need to microwave in 15 second intervals, mixing in between, to get chocolate to melt into the butter.
Add chocolate mixture to egg mixture and mix until combined.
Add oil and mix until combined.
Mix in cocoa powder.
Fold in flour until just combined.
Spread batter evenly over crust. Top with marshmallows.
Bake for 25 - 30 minutes or until toothpick inserted an inch from the corner comes out with a couple crumbs.
Notes
Graham Cracker Crumbs - about 9-10 graham crackers should yield 1 ¼ cups crumbs.Whisk the Eggs and Sugar Well - whisking the eggs and sugar well is the key to getting that thin crackly top on brownies that we all love. Make sure to whisk the sugar and eggs very well until the mixture is pale and fluffy. You may need to whisk for 2-3 minutes to get to that point.Don't Overbake - overbaking creates a dry brownie and we don't want that. The brownies are done when a toothpick inserted an inch from the corner comes out with a couple crumbs. If you insert a toothpick into the center, it should still be slightly wet; the brownies will continue to bake as they cool.