Slice your butter into chunks and combine it with 8 cups of mini marshmallows in a large mixing bowl. Microwave for 2 minutes.

Immediately stir until the marshmallows are no longer chunky and the butter is fully mixed in.

Add the remaining 2 cups marshmallows and 5 cups Lucky Charms to the melted marshmallows and gently fold together until the cereal and unmelted marshmallows are fully covered.

Spray a 9x13 cake pan with nonstick cooking spray. Add the mixture to the pan and gently spread even in the pan.

Sprinkle the remaining cup of Lucky Charms over the top and lightly press to ensure it sticks to the top.

Let rest for about an hour or until set. Slice and enjoy!