Preheat oven to 325 degrees Fahrenheit. Line a 9"x13" baking dish with parchment paper and then cover the bottom with one layer of sheets of graham crackers. Set aside.

In a large microwavable bowl, combine the semi-sweet chocolate chips and butter and microwave on high in 30 second intervals, stirring in between, until fully melted (it took 1.5 minutes in my microwave).

Stir in the brown and granulated sugars and set aside for a few minutes to cool.

Stir in eggs, one at a time, until full incorporated.

Stir in vanilla until well-blended.

Add the flour and salt and stir only until just combined.

Spread brownie batter over graham crackers and bake on the center rack in the preheated oven for 35 minutes.

Remove from oven and scatter milk chocolate chips and miniature marshmallows over the top.

Return to the oven for 10 minutes.

If marshmallows aren't browned enough after 10 minutes, broil for a couple of minutes, checking often to make sure the marshmallows don't burn.

Remove to a wire rack, cooling completely before cutting.