Preheat oven to 350°F (177°C) and line a 9x13-inch baking pan with parchment paper.
Combine graham cracker crumbs, sugar, and melted butter, then press into the pan to form the crust. Bake for 8 minutes.
Sprinkle chocolate chips evenly over the crust.
Add marshmallow crème or mini marshmallows on top of the chocolate layer.
Crumble extra graham crackers over the top and return to the oven for 15–20 minutes, until marshmallows are golden.
Cool completely before slicing. Chill for cleaner cuts if desired.