Mix graham crackers and melted butter until well combined. Add, patting in, to casserole dish. Bake for 15 minutes. Once time is up take out casserole dish. Add sweetened condensed milk followed by mini marshmallows and chocolate chips. Put back in oven for another 15 minutes. Take out and put in fridge or freezer to cool into bars or eat as a S'mores "casserole" Yum!