Preheat oven to 375.

Line a large baking sheet with aluminum foil.

Arrange 16 graham crackers on baking sheet touching side-by-side.

In a small sauce pan, heat butter over medium heat. Add sugar and salt and stir for a minute or two or until sugar is dissolving. (You don't need to wait until it fully dissolves.)

Add vanilla to butter mixture and stir.

Drizzle butter mixture over graham crackers and spread evenly with a spatula across crackers. Bake for 5 minutes.

While baking pan is in the oven, place the two remaining graham crackers in a plastic baggie and use a rolling pin (or a glass) to gently crush the graham crackers. Set aside.

Remove baking pan from oven. Sprinkle chocolate chips evenly over layer of graham crackers and bake for an additional minute.

Remove baking pan from oven. Use a spatula to spread melted chocolate chips across surface of crackers. Sprinkle marshmallows evenly on top and bake for one more minute - just enough to get the marshmallows a little toasty.

Remove pan from oven and sprinkle crushed graham crackers from the baggie over the melted chocolate for garnish. Allow pan to cool to room temperature and then place in refrigerator to allow chocolate to completely set.

Break apart into pieces and serve!