Spray a 9×13-inch pan with nonstick spray and set aside.
In a large pot over medium-low heat, melt the butter.
Add 5 cups of mini marshmallows and stir until melted and smooth. Remove from heat.
Add cereal and remaining 1 cup of mini marshmallows. Stir until evenly combined.
Press mixture evenly into the greased pan using sprayed hands or a buttered spatula.
Let cool completely at room temperature. Cut into squares and enjoy.
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