- 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.