Preheat the oven to 350 degrees.
Line a 9x13 pan with parchment paper and spray with nonstick spray.
Stir graham cracker crumbs and butter together in a large bowl.
Evenly press graham cracker mixture into the bottom of the 9x13 pan.
Pour sweetened condensed milk over the top of the crust. Tilt the pan from side to side to spread it to all corners and edges.
Combine chocolate chips, white chocolate chips and 1 cup of the mini marshmallows in a small bowl.
Sprinkle them evenly over the condensed milk.
Bake in preheated oven for 15 minutes.
Sprinkle additional marshmallows over the top and bake for another 10 minutes or until marshmallows are golden on top. (You can broil for a minute at the end to get them super toasty)
Remove from oven and allow to cool on a wire rack.
Sprinkle a few extra white and chocolate chips over the top of marshmallows. Crumble up graham cracker and sprinkle over the top.
Allow to cool completely before cutting into bars and serving.