Add 5 cups marshmallows, milk chocolate, butter, and corn syrup to a large sauce pan.
Melt the mixture together over low heat while gently stirring with a rubber spatula.
Once melted remove from the heat (place on a heat proof surface) and immediately stir in the cereal and remaining cup of marshmallows. It will be very sticky.
Spoon the batter into the prepared pan and flatten down using the back of your spatula (lightly greasing the spatula can help).
Allow to harden at room temperature for 60 minutes before cutting into squares.
*If you don't have corn syrup use ¼ cup of sugar and 1 tablespoon of water instead.**Store bars in an airtight container at room temperature. I don't recommend storing them in the fridge because they can get too hard.