Lightly grease a 23 by 33 centimeter baking pan and set aside.
In a large pot set over low heat, melt the butter then add in five cups of the mini marshmallows stirring occasionally until fully melted. Once melted, add in the vanilla and salt and stir well to combine. Remove the marshmallow mixture from the heat and add in the graham cracker cereal and stir well until almost combined. Add in the remaining marshmallows and chocolate chips and quickly stir them in then transfer the mixture to the prepared pan.
Press the mixture into an even layer and allow it to cool for at least one hour or until firm before cutting into 24 squares.