Place Lucky Charms is a LARGE bowl or in two medium sized bowls. You will need enough space to really mix the melted marshmallows in there.
In a large saucepan, melt the butter over low heat. Once melted, add in the marshmallows. Stir until fully combined and melted, about 3-5 minutes.
Pour marshmallow mixture into Lucky Charms and stir with a wooden spoon until fully coated and combined.
Spray a rubber spatula with cooking spray then use to pour Lucky Charms mixtures into a 9x13 parchment lined pan. Gently smoosh into the pan until it's an even layer.
Place in fridge and let cool for at least one hour. Then, remove and cut into squares and enjoy!
