Monster cookies are a "kitchen sink" of the cookie world. Take all your mix-ins and make the yummiest cookies - but I've made it even easier by pressing them into cookie bars.
Note: You can use unsalted butter here but with all the sweetness in the recipe it really is good to have to salt to counteract it. So if you use unsalted butter, you can either add 1/4 teaspoon salt to the graham cracker crumbs or sprinkle salt on top after the bars have baked.
Preheat oven to 350 degrees. Place butter in a microwave safe bowl and heat up for about 30-60 seconds or until melted.
Combine butter and graham cracker crumbs in a medium bowl and then press the graham cracker crumbs into a parchment lined 9x13 baking dish that has been sprayed with cooking spray.
Evenly pour the sweetened condensed milk over the graham cracker layer. Sprinkle the oats, peanut butter chips, chocolate chips, and M&Ms evenly over the sweetened condensed milk and gently press in a little. Remember that all of the toppings are approximate so add more or less depending on what you like.
Bake at 350º for 20-25 minutes or until brown. Cool and slice into squares to serve.