Spray an 8x8 baking pan with cookie spray and set aside. Combine the Lucky Charms and Golden Grahams in a large bowl and mix well. Set aside.
In a large microwave safe bowl, combine the marshmallows and butter and heat on high in the microwave for 2 minutes. Watch carefully to avoid marshmallows overflowing.
Once heated, pour the marshmallow mixture over the cereal. Using a rubber spatula, mix well until all the cereal is coated with marshmallow. Dump into the prepared baking pan and push down to form an even layer.
Allow to cool for ten minutes. Serve immediately or keep stored in an air tight container for up to 3 days or in the freezer for up to two months.