Use 2 tablespoons of the softened butter to generously butter a 9x13 (or 13x9) baking dish. This will help keep the cereal bars from sticking to the sides and bottom of the baking dish.

Measure out 7 cups of mini marshmallows to melt in the butter, 2 cups to stir in after the cereal is added and ½ cup to sprinkle on top of the bars.

Add the 6 tablespoons of the softened butter to a 7-8 qt stockpot over medium heat. (You can use a nonstick stockpot to keep the melted marshmallows from sticking to the sides of the pot, but it is not necessary) Stir continuously until the butter is completely melted.

Stir in 7 cups of the mini marshmallows. Keep stirring continuously until the marshmallows are completely melted. This will help keep the marshmallows from burning or sticking to the bottom of the pan. This should take about 5 minutes. Remove the stockpot from the heat.

Stir the 8 cups of cereal and 2 cups of mini marshmallows into the melted marshmallows. Keep stirring until the cereal and mini marshmallows are completely coated.

Spread the coated cereal into the buttered baking dish. (Using a piece of wax paper to press down firmly and evenly could will help the bars be a uniform thickness and make the bars easier to cut.) Scatter ½ cup of the remaining mini marshmallows. Allow the cereal bars to rest and firm up for at least 30 minutes, before slicing the cereal bars 3 slices x 4 slices and serving.