Place the graham crackers in a gallon-sized ziptop storage bag or into a food processor. Smash/pulse the crackers until they become small crumbs.
Pour the crumbs into a large mixing bowl with powdered sugar. Mix to combine.
Melt the butter in a small bowl using your microwave. Pour into graham cracker crumbs, and mix until crackers are moistened.
Line a 9-inch x 13-inch baking pan with waxed paper. Be sure to let the paper come up the sides for easy removal later.
Pour in the graham cracker crumbs and press the crust firmly into the bottom of the pan. Refrigerate crust while preparing the filling.
Filling
Place cream cheese into a large mixing bowl and beat until soft and creamy using a hand mixer or a stand mixer. Pour in vanilla while mixing.
Place chocolate chips and marshmallow creme in separate bowls. Microwave chocolate chips for 1 minute, or until melted. Microwave marshmallow creme for 30 seconds until melted.
Stir chocolate and marshmallow into cream cheese mixture. Mix for 1 minute until well combined. (The filling should be creamy and fluffy like a mousse.)
Pour over graham cracker crust and spread into an even layer all the ways to the edges of the pan.
Chill for at least 1 hour until filling is set and cooled. Cut into 2-inch squares and serve immediately. Top with mini marshmallows and chocolate chips if desired.
Notes
I made a double-thick graham crackers crust for this recipe. My family likes it better that way. You can cut the crust recipe in half if you prefer.