Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking dish.
In a large mixing bowl, cream together the softened butter, brown sugar, and granulated sugar until light and fluffy.
Add the eggs one at a time, mixing well after each addition, then stir in the vanilla extract.
In a separate bowl, whisk together the flour, baking soda, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Fold in the chocolate chips, mini marshmallows, and graham cracker crumbs.
Spread the mixture evenly in the prepared baking dish.
Bake for 25-30 minutes or until the edges are golden brown and a toothpick inserted in the center comes out clean.
Allow to cool in the pan for at least 15 minutes before cutting into squares.