"This is a great, quick recipe for a very sweet treat - no measuring involved! This is so easy to play with. You could make your crust out of chocolate grahams, or add any extra little sweetness you would like."
Preheat oven to 350 degrees F (175 degrees C). Grease an 8x8-inch square pan with cooking spray.
Mix melted butter and graham cracker crumbs together; press into an even layer at the bottom of the pan. Top with chocolate chips, butterscotch chips, and marshmallows. Drizzle sweetened condensed milk on top.
Bake in the preheated oven until bubbly, 17 to 20 minutes.
Let cool, about 30 minutes. To make it easier to cut into bars, cover with plastic wrap and chill, about 30 minutes.