Preheat oven to 350°f and line a 9x9 baking pan with parchment, spray with cooking spray and set aside.
In a bowl whisk together flour salt and baking soda and set aside
With stand mixer and paddle attachment mix together butter and both sugars on med-high speed for about 5 mins.
Add in eggs and vanilla and mix for another minute.
Add in your flour mixture on low speed until just combined
Then add in your graham crackers and semi-sweet chocolate chips and mix for another 10 seconds until combined.
Grab your pan and take half the cookie dough and press into the pan.
Add your marshmallows and milk chocolate chips or chucks on top of dough
Finally top it with the remainder of the cookie dough.
At this point you can add extra marshmallows and chocolate on top before baking or leave as is.
Bake in oven for 25-30 mins. (I usually take them out at 25 mins. for a more gooey middle and they continue to bake while cooling)
Let rest in pan for 20 mins before transferring to cooling rack where it cools for another 20 mins. (If you can wait that long LOL)